When I have the money, I like to order a bunch of cheap games off of
Rakuten. If you're not familiar with it, it's a site through which you can order from various Japanese retailers. Unfortunately, it has some issues:
1. The search function blows. It's best to browse by category
(PC Engine is here).
2. This is a collection of retailers, not one store, so keep in mind how many retailers you're buying from when trying to figure out shipping. Usually, I just go to a store page that I keep seeing on a bunch of games and just browse through there.
3. This all ships from Japan, so you really need to buy a bunch of stuff at once to make the shipping cost worth it.