I think you'll have to call Wyndham Rewards to ask, possibly elevate to a supervisor if you don't get a good answer from the front-line agent..
I've had the same problem with a Howard Johnson in Argentina about an hour outside of Buenos Aires. No availability ever on the WR website, but availability through third-party sites. But in my case, after researching more, I realized I didn't need a stay at that location anyway, so I never took the time to dive into why this was happening.