I have found some realtors that specialize in Adult Family Care Homes in Washington state. They list homes that are currently filled, licensed and empty as well as homes that are potential AFH's. I will put their link at the end of this post. If you are looking to purchase, these realtors might be your best net as this is what they specialize in. I have never met them, only found their site online and looked through it. It looks like a very well laid out and organized web site, easy to find what you are looking for. I saw that they have homes listed south and north of Seattle.
If you have any questions about buying or leasing an AFH, email me at afhwa@yahoo.com and i will do my best to help answer you, as I have been licensed in Real Estate in both Oregon and Washington and have been through AFH rehabs and retrofits.
Again, here is the link to the Real Estate web site