There are forums specific to a given camera (Rollei forum, Hasselblad forum, and the defunct Mamiya boards), but no strictly gear-oriented equivalent of the RFF for medium format.
At any rate, all forums cross purposes: APUG has all sizes, all techniques analog; RFF has all RF (incl. MF ones) in addition to TLR and SLR sub-forums; photo.net has its own latitudinarian selection, the Zeiss Ikon users cross both RF, SLR, all sizes, and so on.
In the end, you can discuss MF-related issues everywhere. Some of us actually are denizens of multiple forums. In the end it's about choosing your gang: you may prefer discussing MF on a given forum rather than on another.
Choose your gang.