The easiest way to find STi suspensions on eBay is this:
(1) go to ebaymotors.com (2) click on 'parts and accessories' (3) click on 'suspension and steering' (3) enter 'sti' into the search window (4) voila, start your bidding
or, just enter 'sti' at ebaymotors, and you will see everything sti on eBay...
This is the auction that I went for... The buyer ended early, but i purchased the setup from him afterwards for $540 shipped to my door: