Normally I wait to do a post on a player coming to the US until they've actually signed a contract with a team. I've decided to go ahead and do one for Tanaka because I think the interest is probably pretty high right now. I'm amazed that I have not seen the usual bullsh*t on Ebay yet - no "GTC" "Future Stars" cards or OMR "Top Prospect" cards (showing one NPB player and two amateur players named for high schools). Everything that I've seen has been legitimate and only a handful incorrectly label whatever card they're selling as a "rookie card". I expect that that will change when and if Tanaka signs with someone. (There was one seller selling a couple packs of 2008 Calbee that implied in his description that Tanaka would end up with the Yankees, which I felt was a bit premature.)
Tanaka was drafted by the Eagles in the first round of the 2007 draft (held in the fall of 2006 of course) after a stellar high school career at Komadai. His first BBM cards are in the Rookie Edition (#40) and 1st Version (#211) sets in 2007. (I'm not sure which should be considered his BBM "rookie card" - both sets were pack based, nationally available sets. Rookie Edition came out in February, 1st Version came out in April.) His first Calbee card was also in 2007 (#158).
Tanaka has been in every 1st and 2nd Version set since 2007. He's been in every Calbee set since then also although he did not have a "regular" card in the 2012 set - just appearing in the "Title Holder" and "Opening Day Pitcher" subsets. He made the All Star team every year he's pitched in Japan except 2010 and so appears in each BBM All Star set from 2007 to 2012 except 2010. (Since he was elected as a starter for the 2013 All Stars, he appears in the 2013 Calbee All Star subset.) The Eagles made the Nippon Series just once ever and unfortunately it was the year (this year) that BBM decided to stop doing the annual Nippon Series set. So there is no Nippon Series card for Tanaka.
Tanaka has played for the Japanese National Team three times as a professional - the 2008 Olympics and the 2009 and 2013 World Baseball Classics. He's got a card in the 2008 BBM Olympic team set, two cards in the sets that Topps did for the 2009 WBC, and he appears in the 2013 Topps Tribute WBC base set. (And obviously there are a number of parallel and memorabilia cards associated with the WBC sets.)
In addition to his appearances in various sets, there have been three sets that are completely about him - BBM did a "biographical set" for him in 2010, Sports Graphic Number did a set devoted to him in 2012 and BBM put out a set about a month ago to commemorate his undefeated season.
As always, this is not meant to be a comprehensive list. Check Sports Card Forum's Inventory Manager for a more complete list. (And keep in mind there was an outfielder for the Tigers who was also named Masahiro Tanaka, so don't be surprised when you see some cards from the 1980's listed.)
Here's some example cards:
|2007 BBM Rookie Edition #40|
|2007 BBM 1st Version #211|
|2008 BBM Japan National Team #JPN07|
|2009 Konami Baseball Heroes Black #B09B082|
|2010 BBM 2nd Version #785 (Twin Gem subset)|
|2011 BBM All Stars #A17|
|2012 Calbee #OP-05 (Opening Day Picher subset)|
|2013 BBM Classic #055|