Best place in seattle is Little Amazon. Although it's small, a bit stinky, and not the best on animal care, it's the only place in Seattle where it is consistantly possible to get anything other than veiltails. Usually they have "half-moons" for 14.99 - be aware that these are mostly super deltas, though, and not true halfies. They usually have a few other varieties as well. Last time I was up there, they had a huge stock of double tails. It's on aurora ave., just before the 105th street (AKA Northgate Way). It's about a 15 or 20 minute drive north from the stadium, on the east side (which is the right if you're going n on Aurora from downtown) of Aurora ave, also known as highway 99, or simply, "99". If you think you might be heading down to Tacoma, let me know - There's a place in Tacoma that has big, beautiful wild-type shorttails.
I know a place that's about 20 minutes east of seattle that has a truly impressive stock of different cories, too, if you are interested.
Oh! I just realized - If you are going to be in seattle the weekend of august 14, the betta show will be going on!