I wouldn't recommend PlayStation games in universal games cases.
Which kind of Nintendo games are you using? If it's NES, I again wouldn't recommend universal game cases due to the amount of modification needed. Go with the Shadowfox cases instead (customgamecases.com).
However, if you really want universal game cases, mediashelving.com is your best bet if you live in the US. Outside of the US I hear it's pretty difficult to find a place that will ship to you. Ebay might be the easiest, but it will probably be expensive. More reason to look at Shadowfox's cases.