REI and Feathered Friends have Mammut gear, but I doubt they would have those items specifically. Backcountry, Moosejaw, and REI all have great online return policies. You may be able to try some Mammut stuff on at REI just for fit.
Regarding the pants specifically, I have those myself. They fit pretty much exactly to the measurements that Mammut has on their site. I bought mine from Backcountry. They are pretty sweet but a little bit of a PITA if you need to make any adjustments in the alpine. Between the buckles, zippers, gaiters, and velcro, there is a lot of things to undo and redo. When they are on properly they are awesome though. The fly is somehow in a kind of weird location though...hard to pee out of them for me. (Or maybe my penis is in a weird location?)