Good news from a frame builder
I usually hang around in C&V or frame builders and figured I should chime in here after reading a couple of threads. Using technology from all the different genres of cycling you folks can have bikes that don't dissolve when you drop the hammer. It may be hard to find a off the shelf carbon or lugged bike but custom alloy steel or aluminum is no problem. I built a aluminum MTB frame for a 450# fella that was a pretty hardcore rider and a chopper for a famous 475# athlete. The MTB frame weighed around 6 lbs. I am showing you this one because I built it twenty years ago and hasn't been back for repair!
, on Flickr
If you are over 400#
Hadley through axle hubs (there may be others) with steel axle, 26" high profile Alex rims
custom 4130 or 6061 frame/fork with long head tube (less bearing leverage)
You may still have difficulty with chains and freehub bodies/pawls but the hub will last and can be serviced. Many bike shops these days are tied to a single brand and can't even make suggestions outside their product lines. I am starting to get jobs from people who are only slightly larger than average who tell me that bike shop employees completely ignore them when they walk in the door.