I ended up just ordering one of the pads from Poland, with the intention of modding it to work with the PS2, and then I ended up installing Stepmania on my old, generally-useless Mac mini and downloading all of the songs from the PS2 games that I’d rebought, making the PS2 entirely redundant anyway. Rumor has it that the Polish pad manufacturer is working on a native PS2 control box and when that comes out I guess I could buy one but jeeze, Stepmania on the Mini looks and plays so much better than the real thing on the PS2 anyway, so why even bother?
Plus, Stepmania has a huge community of people adding more music all the time, and maybe this’ll encourage me to make some packs of my own stuff. I bet Sliced by a Mandolin would make a great DDR track.
Oh, and even after shipping, the pad from Poland still ended up cheaper than any of the domestic options I could find, DIY kits included.