Tee's USA has Bride seats, or check out Sparco stuff. Sparco is here in the USA, and fake Sparco is not really a problem in the US. If you want stock STi seats there are eBay vendors who carry them. As for good seats which will fit your car well, take into consideration whether you want adjustability, what materials you want, what type of materials are used, how heavy they are, there's a lot of variables, and therefore a lot of seats. There are FIA approved racing seats from $245 up in Sparco's lineup, and Bride is from $299 up, for FRP and without adjustment. For any exotic materials, you can spend up to about $3500 for some mirror-metal painted Kevlar Bride Gias, or some Maple Leaf emroidered Cugas for about the same dollars.
Sparco has an excellent reputation, as does Bride, but there are a lot of fakes, be careful to buy from a reputable dealer. As far as I know, Tee's is the only licensed distributor of Bride Racing in the USA. As for Sparco, they have their own online catalog and ordering system.
You have to pick what you want. There are so many choices. Just think out the whole system, what harness kit you want, how you will mount the harnesses, whether you are going with a cage or harness bar, all that stuff. Most racing seats don't "get along" with factory seat belts. It ends up being the installers' woes to have to disable the signal from the factory belt (you can get NZKW rail frames and keep them!) and tuck that into the carpet.
If cheap but good stuff is what you are after, try eBay and run a search for "Seats WRX" then get yourself some rails and have fun!
I recommended the brand named seats above because they are known to be safe and tough, and will look good and function properly for many years. Mine are 4 years old (Bride Gias Kevlar), I got them the year they were released in the US, and they still hold very solid in their second car.