I've never modded a PS2 or used a swap disc with one, but I have bought Japanese PS2s before so I can help with that
Apart from eBay you can buy them from
Play-Asia they're not cheap but they are new and in stock. It's not an easy thing to find nowadays, we're kinda at that point where they aren't old enough to be retro and have a lot of import interest. You could also import a first-run Jp PS3 instead, as those have proper hardware backwards compatibility (tested myself on 100+ games!).
I do like dungeon crawlers, but I've only dabbled in Wizardry so I can't help with Busin, sorry.
