If you need a stock part (maybe you’re going back to stock for emissions testing or because you’re trading the STI), but don’t want to deal with dealer pricng, I found a decent salvage yard that has a good internet presence.
Oak Leaf Salvage is located in Wisconsin but will ship parts. They’ve a basic and advanced internet search feature, as well as an image search feature (in case you don’t know the name of the part). For parts that aren’t showing up in the search queries, a contact form pops up that will allow direct correspondence with the salvage yard.
This particular salvage yard does have decent Subaru exposure (they post to IWSTI).
I’ve used salvage yard parts before. I had a Mustang that burned out a power window. My dad got a motor from a salvage yard that was local to him and I had it installed by a mechanic. Never had an issue with that window again. Salvage yards usually verify that the parts work. If the parts are electrical, they can be tested with multimeters — if the part is mechanical and doesn’t have damage, it should work.
This is another parts option that I thought I’d share. If Craigslist or eBay isn’t working out for you, try this place or any local salvage yard.