I've used buyee.jp in the past. Mainly bought photo gear through that site, though. I have seen a decent amount of vintage Mac stuff on the yahoo! Japan auction site, which Buyee usually is used with, though.
I’ll second buyee.jp. It’s fairly straightforward to set the language to whatever you prefer and to make purchases. At the beginning of the year I purchased a IIvx and a IIcx (restoration stories coming soon) and even with shipping the prices were comparable to FleaBay - of course this was before the crazy tariffs for us in the US.