In case it wasn't obvious from johndoe's post, you are looking for S5, not S4 injectors. That's how they're commonly listed in the ads at rx7club, so I'm just throwing that out there for anyone who isn't up with RX7 lingo. S5 TII injectors are the high impedance 550s.

Got my set of 4 for $80, uncleaned of course, and a couple had minor cracks in the pintle caps that will be replaced when I send them out for service. If they're already cleaned & flowed, $120-150 is decent depending on how fast you need them. If you can't find any in the ads, just post a WTB and you should get some responses over there (rx7club).