Easterns will flat out drive you nuts !!

Just thought I would warn you, they call them "phantoms",
You would save gas, time, and effort if you go ahead and hunt the other species.

If you seriously are committed to hunting Easterns, plan on spending more time attempting to locate these birds than to actually "hunting" them,
look at the harvest reports on WDFW website, pick an area and start scouting now.
Find gated roads, and search for sign, get out of your vehicle well before daylight and cover ground.
Capital Forest has birds, Vail Tree Farm has birds, I have heard Mason County has some.......
They are on both sides of I-5 all the way south from Thurston county to Cowlitz, and maybe to Vancouver, but finding small flocks scattered over all that real estate is going to be your biggest challenge.
Almost nobody is going to give up their area, it is too hard to find one, then to share with someone they don't know.....