I saw a sign just the other day that says "Southwest Transfer Station south of Sunriver: May 22-June 5 (Wednesday-Sunday) 8 a.m. to 4 p.m." if you still need to get yours done. The sunriver one was on may 7th and 8th.
The dates have all passed except for the La Pine Transfer station takes it through June 4.
Thanks! Your answer is awaiting moderation.