Westcoast has a store in Bellevue now, they have ARs there too, though you can only look, must be purchased through their Issquah store. (you can thank the ******* mayor of Bellevue for that)
If you just want to look but not buy (and be truly sticker shocked) check out Wade's in Bellevue. Big selection, even bigger prices. Like way bigger. Did I mention how overpriced everything is there? But yeah they got tons of stuff, and a nice range.
If you want to go a little further south, Federal Way Discount Guns has a pretty good selection of ARs (and other cool rifles like SCAR, F2000, FAL, Barrett, etc) and good prices if you're looking to buy.