Seattle also has the same department stores like Nordstrom and Macy's with their Petite depts, and chain stores (Banana Repub, J.Crew, etc.) that most cities do.

So, I will mention instead the type of clothing particular to Seattle.

For the longest, I've been looking for travel pants to fit my 5 foot, 96 lb, 34" hip self.
You know, the kind that has a lot of pockets including a security zip pocket, made in a quick dry fabric that doesn't wrinkle? Something non-matronly?

With a 2 1/2 week trip to Europe coming up where I would hotel hop every 2 or three days with only carry-on luggage, I needed something I can wash in a sink and hang dry overnight.

Enter REI.
The flagship store happens to be in Seattle so I checked them out.
Their private label REI brand Willow convertible rollup leg pant comes in 0 Petite.
OMG, it fits!
North Face label's drawstring waist, also a roll up leg pant, comes in a 0 Petite and it fits and looks even better than the REi pant! I bought 2 of each. Also available on website.

Rain gear ( rain jackets, water proofed insulated jackets) from Eddie Bauer. Yes, the Petites are online but I thought I'd mention them since they are a Seattle manufacturer.

If you can afford them, All Saints Spitalfields, a UK brand. Love, love this brand. Think rocker marries goth. Hella Expensive but if you are a fashionista, you won't be able to resist.
They opened a shop in downtown Seattle and there's one in NYC.
I had tried on a military cut fitted black jacket in London and they run small. I couldn't even button up the jacket around my 31" chest. That has Never happened. I'm not sure about the size range they carry in the US shops, though.

I will add more if I come across other unique to Seattle shops that carry petite-wearable togs.