Most engines that have been swapped so far have come out of wrecked WRX's, which seem to be getting wrecked left and right.
Actually, I did answer your question, but you complicated the querry by not having the correct information. In my post above, I specify that many guys are swapping engines from wrecked US SPEC EJ20 ENGINES.
If you want an engine from Japan, specify whether or not you want an EJ20-K (closed deck, 1997 and prior), EJ20-G (newer engines, open deck), or even an STi engine! It all depends on how much money you want to spend.