Draftable collegiate catchers seem to be a vague rarity for whatever reason; many solid collegiate catchers decide to go into the industrial leagues instead, probably to play for a few years until their knees give out and then have a guaranteed nice office job to work at for the rest of their career.
Sanspo actually sorted their draft list by position! So I can say that there are only 9 catchers on that list, and all are ranked C prospects except the "Big 3". There are two others who have entries on Draft Reports, at least:
Ichiro Matsushita, Kansai Gaidai University. A very INTERESTING player, Matsushita spent 6 years living in London because his father had to move there for work. He came back to Japan for high school, and was the captain of the baseball team at Rokko Island HS -- but they never got further than the 3rd round of their prefectural tournament (not surprising, Hyogo is one of THE toughest prefectures in Japan to crack). Then he went to Kansai Gaidai University, where he apparently is majoring in English... which he is naturally fluent in after living in England for so long. If I were him, if he goes through Draft Day unpicked, I'd totally try for some sort of playing option abroad, although he's awfully small at 172/77, that's barely bigger than I am. But he is the captain of his team this year too, and he had a very good spring season, batting-wise. I dunno.
Kiichi Shirakawa, Kyushu Sangyo University. Also team captain, he was league batting champ in the spring with an ungodly .590 average (23-for-39) and a 1.634 OPS, and got invited to the WUBC camp this summer though he didn't actually make the team. Shirakawa's one big point in his favor could be that he's a lefty-batting catcher, though.
As for the Big 3 themselves, they are, in draft pick probability order:
Shota Koike, Aoyama Gakuin University
Takanori Satoh, Toyo University
Tesshin Sameshima, Chuo University (also team captain)
And having seen all of them in person a few times, I actually have taken photos of them! Hooray!
Charging a bunt.
Charging a foul ball.
Koike is from Tokyo, and he played baseball at Shutoku Gakuen JHS; as a 3rd-year he batted 8th and caught, and his team made it to the finals of the national JHS baseball tourney and lost. (One of his Shutoku teammates was now-Toyo catcher Takanori Satoh, who batted 7th and played RF.) Rather than go to Shutoku HS, he continued on to Joso Gakuin in Ibaraki for HS, and since they do indeed go to Koshien almost every year, he played at Senbatsu in his 2nd year and summer Koshien in his 3rd year, losing in the first round both times.
He got to Aoyama Gakuin and pretty much was the team's starting catcher from his first semester as a freshman, and he hit a grand slam in his very first game. Had some shoulder trouble as a sophomore and mostly entered games as a (crappy) DH; healed up from that and went right back to kicking ass and taking names. He was on the national team for the Japan-US college tourney last summer and also represented the collegiate team for the U26 NPB game, and was also on the national team for the WUBC this summer.
Unfortunately, shortly after filing his registration for this year's draft, he broke a finger on his right hand and couldn't play in any more games this year. However, I have a hunch that he'll still get drafted; he's just a solid catcher and a solid hitter, comes from a really good baseball pedigree and has succeeded at every level he's played at. He's generally listed as an A/B prospect based on his arm and defense and having a reasonable if not spectacular bat to go with them.
Takanori Satoh (for the record, he is 佐藤貴穂, not to be confused with another Takanori Satoh, 佐藤貴規, who is Yakult's Yoshinori's little brother and an outfielder at Sendai Ikuei)
Satoh catching a pitchout to a bunter and trying to throw out the runner.
Satoh at bat.
The guy on the left is Takahiro Fujioka, and the guy on the right is Satoh, having just finished pitching and catching an 11-inning game against Kokushikan together.
Satoh is also from Tokyo, and like Koike he played baseball at Shutoku Gakuen JHS; as a 3rd-year he batted 7th and played right field, and his team made it to the finals of the national JHS baseball tourney and lost. Also like Koike, he decided not to go to Shutoku HS but instead went to Saitama's Kasukabe Kyoei, which despite being one of the Saitama powerhouse high schools, goes to Koshien a lot less than one would think. Yet they did go in 2005, and Satoh batted 7th and played 3rd base, and went 3-3 in their only game... where they lost to Osaka Toin. It's a little scary looking at that lineup now; Toin featured the bats of Sho Nakata (Fighters), Ryosuke Hirata (Chunichi), and Takanobu Tsujiuchi (Giants) was pitching. Satoh, to his credit, was 3-for-3 with a walk and a sacrifice in the game.
Satoh continued on to Toyo University, and in the winter of his freshman year, due to having a strong arm and good baseball sense, was converted into a catcher, learning from Shota Ohno (now Fighters). After Ohno left, Satoh became the starting catcher for Toyo and helped lead his team to several championships; Satoh batted .419 in the spring 2010 semester and Toyo won the national tourney, and at the time of this writing he is batting .333 in the fall 2010 semester, good for 3rd in the league. He was on the Best Nine list in spring 2009 and spring 2010, and also played on the Japan team in the Japan-USA college tourney in 2009.
For whatever reason, Satoh isn't thought of as being as good a prospect as Koike; I think it might be more that Koike has been catching forever and ever and has so much experience at the position and has proven himself at so many levels. On the other hand, Satoh might be more versatile, should a team choose him; the Fighters in particular have a habit of playing their extra catchers at 2nd base and other places in the outfield to get them into more ni-gun games. Honestly, I'm not a scout, and I got a vague sense that Satoh might not be as good at handling pitchers in difficult situations; I noticed I don't really have any pictures of him going out to the mound to talk to pitchers, which may or may not indicate anything.
Like many of the others going into this draft, being part of the "Saitoh Generation", Sameshima's high school career also crossed Saitoh's -- in the semifinals at Koshien, where Saitoh struck out 13 people (including Sameshima three times) and beat Kagoshima Kogyo to go on to the finals and face Tomakomai in that historic dramatic finale. Sameshima was, for his team, both the captain, catcher, and cleanup batter.
When he came to Chuo, just like Koike, he became the team's starting catcher from the first semester of his freshman year -- the first guy to do that in 10 years at Chuo (the last one before him was Shinnosuke Abe). He'd still be the captain, catcher, and cleanup (and more alliterative in that Chuo starts with a C too) if not for the fact that they have a 100-kg first baseman named Seiya Inoue who fits the cleanup slot a slight bit better.
Sameshima was on the Japanese national team in high school, but hasn't actually made the cut for any of them in college, probably thanks to the above two guys, so he's slightly less-known to general baseball fans, but on the going-pro front, has undoubtedly been benefitting from all of the scouts coming to watch his team's ace Hirokazu Sawamura.