Nobody reacted to my "any old machine with ZZ attachment" idea so maybe it was a bad one, but I read that this attachment is pretty great.
Regarding the 206, it uses the same needles as my 319, and I had no trouble find them. Just to be safe I bought a 10 pack of each size (12, 14, 16), but Schmetz is still making them. This machine (319) is really nice to use and does a zillion different patterns. The 206, 306 and 319 are all very similar. The body of the machine is "lightweight" aluminium but it still weighs a ton (I have it in a cabinet).
I'm on the lookout now for a reasonably priced ZZ attachment so I can try out my 201 and 66, but from all accounts they're excellent.
http://www.youtube.com/watch?v=mqmVKBENpVw The Zigzagger appears to move the fabric rather than the needle, so you won't need to buy a new base plate or modify the needlebar. Anyone this time?