Which side of the state is Kennewick on? Oh, hell, I'll check a map....
Heck, the Kennwick-Richland-Pasco area looks large enough to have a poly community. I'll suggest using OK Cupid or some other poly-friendly personals site to check for poly folk in the area. I suggest also checking out Seattle and Portland for poly groups, as they may have members from the whole region, meaning some relatively close to you.
And remember that there are poly folk who still haven't figured out that they're poly. They only figure that out when they get interested in somebody who is already actively poly. So the local singles crowd may produce suitable partners of whatever sort.