Before 29'ers became the in thing with mountain bikes, such bikes with 29 inch wheels tended to be marketed as 'Clydesdales' at tall and large riders. A good number of brands had specific models, but now that they are all selling so many 29'ers they seem to have dropped that all together.
I think the wheels are actually the most critical thing you need to get right as they take all the weight and the spokes may go. This may well mean getting a hand built wheel which can easily be tailored to a larger rider.
The other area of course is suspension. A lot of bikes have air suspension these days, so you would need to be sure you are within the operating limit. With spring operated forks, its possible with some models to put in stronger springs to cope with heavier riders.