The psone games I actually like I already still own luckily, BUT, check out flea markets, garage sales, book and game shops, places that sell traded in movies and games can sometimes be a good place. Amazon.com... google shopping.
//--This next part has nothing really to do with the subject unless you want to buy stuff online but can't since you don't have a credit card. Ignore if this doesn't apply--//
If you need a credit card for the cheap website game stores, walmart sells these prepaid ones that work well, but they charge like 8 bucks to put money on em, and they will charge out quick with stupid fees. So, "cash a paycheck" into one, but tell them you want ( <paycheck> - <how much you wanna spend online> ) in cash and spend everything on the card that day, that way you don't pay 8 dollars (it's free if you cash payroll into the account) to put money on your card, and they don't get any of their crazy fees in there.
I only do this since my credit union doesn't do the debit card thing :P
PSTWO Slim Silver v15 NTSC/US
PSP Slim Silver Daxter Edition 5.00-M33 custom firmware
Xbox1 60gb Hard drive all softmod with UnleashX
Xbox1 Stock HD Red/Black Case Softmod UnleashX
Fire Red GBA-SP