Big O and Tire Pros should have no problems. Discount Tire was a ****** bag about mounting 315/70/17 BFG ATs on my boss's F250 on stock rims, here's the catch, it already had that size on there and I already had the replacement tires, I was just trying to pay them for the mounting and they said no.
One exception, near the Scottsdale Air Park there is a Jeep guy named Rick Beer who is an avid offroader who will take care of you. Depending on what part of the valley you live in I suggest C&R Tire off Tatum and Bell (they got the BFGs mounted and I'm going to start using them more often, guy said he will be able to mount my 37" Toyos on my 22s for my Superduty when I need it done), Gunnel's Big O in Mesa on McKellips or Big O on Miller and McDowell. Also there is two 4 wheel parts stores in the valley. They WILL price match and usually have good deals.