There are actually several gun manufacturers that exist, that we don't have a subforum for. It's not possible to catch every brand.
For now, Mossberg doesn't have enough of the market to justify a subforum. Sorry.
Hi Point, Tangfolio, EAA, Canik, SCCY, American Tactical Importers and Chiappa are other examples of gun brands that would not have enough traffic to warrant their own subforum yet. If any brand would get one soon, it would probably be Canik.