Go to www.mangahelpers.com Click on Download Manga, and then go to [JP] RAWs. There's lots of manga on that site. I hear some of the fan translations are not so good but it doesn't matter if you're going to read the Japanese anyway.

You might just buy some manga that's in Japanese <try ebay>. (Ones that have been professionally translated are best, so you can compare your translation with one that is definitely correct). That's what I did.... I got a lot of Fruits Basket manga in Japanese, read the English ones, and then worked on translating the corresponding Japanese volume. Plus, if you get a lot <with reasonable shipping>, it could end up being less than buying the English version! ^-^