They're on eBay for under $20...

2.5'' V-BAND STAINLESS STEEL CLAMP FLANGE TURBO EXHAUST:eBay Motors (item 320430025065 end time Oct-29-09 18:43:05 PDT)

Do the ones used in plumbing use any sort of o-ring? I had a v-band exhaust on my S13 and S14, and it fit fine for exhaust, no leaks, but I don't think the fit was nearly tight enough to not leak at all. Especially under vaccum like an IC set up would see.