Posted a wanted ad on MSCCNC forum and found some stock 14" the same day. Aluminum "daisies" with tires that should still have a few races in them, all for a hundred bucks!
Will try to pick them up when I'm back in town next week. Really, really itching to go to an event now.
[edit: Sat, Nov 10, 2007. Picked up wheels on Friday evening. Indeed, there *is* a way to fit four wheels in a Miata: One in the trunk, one behind the seats, with the top up, one behind the passenger seat, and one in the passenger seat. Here they are]