I recall using landwatch.com when I was searching several years ago, you can select areas and put in minimum acres. Lately prices for most real property has skyrocketed, and you'll definitely want to find something with an existing, permitted well as Washington passed the Hirst decision that says a county can deny a well permit even for personal home use if it impacts existing properties:
https://ecology.wa.gov/Water-Shorelines/Water-supply/Water-rights/Case-law/Hirst-decision
The Cob Cottage company (
http://www.cobcottage.com/ ) is on a 400+ acre property which I heard is in a land trust, and it sounds like they are looking for someone to purchase that trust so they can remain:
https://www.gofundme.com/f/save-cob-cottage-company and due to the trust it might be affordable per acre compared to everything else right now, assuming the owner is trying to sell. CCC uses a year-round creek for their water and it's in a great location a few miles from the coast in SW Oregon.
I've heard Washington can be picky about water rights, I would contact each county and ask about their rules on water retention like rain gutter storage or using pond/creek water. Once you have some that meet your needs, you can check sites to see what is out there. Owner financing is usually the only option if you can't pay cash.