A really good store for older, hard to find stuff is surpluscomputers.com. They just closed their retail store in San Francisco, but you can get older sound cards and so on brand new. I picked up an old IBM 486 at the Goodwill just to tinker with (that sucker was almost $4,000 new) for five dollars, and bought the old Soundblaster card for it for $10 from them. They still have their online store.