CL, can always find 55G food grade barrels, another option is any local Feed stores. they often have used barrels as well.
last, try your local county public works department, sometimes they sell cheap for rain barrels, so your not collecting rain , just RO lol tell them RO is run off from roof LOL
Hit up cash and carry! they have a good selection of these kinds of things. or there are a couple restaurant supply stores downtown seattle that have good prices. also a brute garbage can from home depot works well.
I would say go to the Cubby & Tubby gardening center up on Aurora (99) in Shorline/Lynnwood area. They have TONS of food grade water storage tanks from a few gallons up to several hundred gallons in size, but that would be a long drive for you from Oregon.