That was easier than I expected - I only had to look as far as my rss reader, where what I was looking for on the excellent Marine Blue blog. The author published a retrospective on Tanaka after he was released by the Marines, which includes abbreviated stats and a number of photos. Highly recommended. The author published similar retrospectives on all the players that left the Marines over the last offseason.
Here are the stats, re-purposed in English.
Note that numbers prefixed with "E" in the appearances column are Eastern (minor) League appearances. I've italicized his 2003, top-level appearances. You can learn a lot more about the Japanese minor leagues on Deanna's site.
Generally speaking I don't take minor league stats too seriously. There are too many things to discredit them - the player might be working on a curveball, might be facing guys on rehab assignments, might be playing in front of an inexperienced defense. But from a young pitcher with eight years experience, I'd like to see some signs of improvement and a decent K rate, both of which are missing from Tanaka's resume. Maybe he'll take to US coaching and conditioning and improve, but the numbers would seem to indicate that he has a long way to go.