You could try my local dealer, Le Mont Saint Garage. Email email@example.com
, he may be able to help you (tell him Mark Page referred you). I guess prices would be slightly more than advertised due to the cost of getting the parts sent to Guernsey then on to you. For the STi airdam look under 'front underspoiler', I think it's the same although it may not be, having looked at foresterperformance's site. I've also seen the Prodrive WR version of the forester, it basically turns it into an STi more or less.
I'm not sure, but I think it's been dropped from their website now though.
I've a couple of piccies of my car that I'll post sometime too.
If you thought finding American forester stuff on the web was difficult, it's even worse over here!!