#1 My understanding is it is illegal to sell native fish in a pet store and I work in one.
#2 Here is your list of banned fish and other critters
WDFW Aquatic Nuisance Species
#3 Get a fishing Licence and read the rules then good luck hunting.
If you want to be a purist there is some bad news:
"Before the late 1800s, the only resident freshwater
fish living in Washington State were trout (cutthroat and
rainbow), char (bull trout and Dolly Varden), nonanadromous
salmon (kokanee), whitefish, burbot,
northern pikeminnow, suckers and smaller fish generally
unimportant to anglers."
Now as far as keeping them they call the freshwater fish in Washington state Warm Water but in truth they will do better in an unheated tank. Guess they think it is warmer than the ocean.
Now for all the species that can be found sadly this is just the game fish I have had a killer time finding the non game fish list:
WA Warm Water Fish.
I do know there are some sculpins that are native and a good place to start your search is
NANFA
Here is their check list of all
NA species
I know all of this because I want to setup a NA Native tank or 2 and I'm looking at the pygmy sunfishes myself and I also live in Washington.