Michael, since there's noone here can give you any advise in the local area, I will.
Discount tires at Bellevue generally doing good jobs on mounting tires. I had mine mounted there and Polar did. They also offer Road Hazard Warranty which, with the late poor road construstion around S. Seattle and you are running expensive tires, I strongly recommend you buy it. They also matching internet tire rack price, do some print out and have them match it.
However I do have my buddy who owns a body shop, who does tire mounting as well. (He will probably won't be able to help you much on getting tires, but he gives me smoking deals on mounting and balancing tires.) all mine, Polar's and freelance's track tires were mounted there. and get this, they sometime worked over night, so if you have a tight schedule, you may do that after your working hours. (however, I believed he's doing buddy's deal, so no responsibilities, no suing ... bra bra bra...) But, if I trusted him installing my track tires, you shouldn't have any worries on street.
I had also have good experience with one father and son operated small shop in Renton. I believed it's called Mc Millian or something, I couldn't find it in yellow page. Their store are at the Rainier Ave N. and they used to park their Rally prep'ed Subaru(very old, not wrx) outside the store. They do a lot of big blings and Spinners, (hey's it's Renton
) and I had they fix my wheel in my daily driver(in a gettho way, big hammer) in it works fine.
I guessed if you really want the S03, Discount tires at Bellevue will be your choice. They have one in NorthGate and other in Renton even though I don't have any poor experiences with them, people worked at the Bellevue store seems to have more experience and by comparison they worked more on expensive wheels.
*** BTW, if you are looking at the Costco tire installer in Issaquah, unless you don't care about gouges, I have Polar's old S4 rims (on all 4!!) to confirm the bad experiences.
** I also suggest you that go find a shop who don't mind you stand and look at their work progress, so if they did something wrong you'll catch them on the spot. If you had seen how tires mounting work, it's really not rocket science and you can tell your installer is experienced or not right away.