I'm a big *and* fat guy, though not tall- 5'11" 290 lbs and a broad chest/shoulders, 40-42" waist. I've actually found that most brands fit me in XXL and even XL. I do have problems with sleeping bags with a narrow cut- Lafuma, Summerlite, etc- my shoulders are too broad to get into my usual sleeping position with the bag fully zipped up. Some of the European brands don't work well for me- Rab in XXL just squeaks in around my shoulders and chest and too much space around the belly.
The only thing I've ever been frustrated with is an extensive selection of pants. A lot of the pants recommended to me by OR, Arc'teryx and others top out at a waist of 38. Not the end of the world, but often makes me settle for something that somehow falls short. Also, most pants seem to come in a 32" inseam and nothing else. A lot of brands have a Regular 32" and Tall 34" inseam, but it's a lot harder to get my 30" inseam.
The only bit of gear I've been entirely thwarted on is a set of light gaiters. I've big, muscular calves that are too big for every pair I've been able to try on.
First Ascent is one of the few brands with an extensive collection of tall sizes, and so much of the stuff that has gone on 50-80% clearance is only available in XL and XXL. :)