Well, figuring out the japanese PSN thingy isnt that hard. There are quite a few guides out there how to make an account.
And as for the cards, just get paypal and buy the code from ebay or one of the code online shops out there. Worked for me at least.
Click buy, wait 5 mins for the mail, have fun with your psn stuff :O
Though another possibility would be, if someone would make a guide on how to skip through story mode fast to unlock the charaters.