I am in no way connected to these sites, nor have I ever visited them, so I have no idea what they are like, but here are a few that are listed online:
mthfr.net/forums/mthfrsupport.com/forums/forum/mthfr-support-forum/goo.gl/udYrDY A Yahoo group for MTHFR.
mthfr.proboards.com/ Hopefully you will either find what you wish in those links or will be able to find information in those forums for the forum you really wish to find.