Lots of good stores here in Vegas unfortunately not very many AR's for sale. Accessories no problem but as far as complete new AR's - forget about it. The stores mentioned so far are all good, one addition is Nevada Pistol Academy on Blue Diamond. Machine Gun Kellys on Sunset (next to the airport) has about the best selection overall right now.
As far as shooting goes there are several indoor ranges that all rent (Nevada Pistol, The Gun Store, Discount Firearms and American Shooters Supply). When you get here just look in the phone book under "Guns" for numbers and directions. As far as the desert goes you can no longer just go out anywhere and shoot (thanks to the BLM). There is an outdoor range in Boulder City that has a free public range - no rangemaster, bring what you want, usually only one or two other people there - everyone is always totally professional. Check out www.brpc1.org or stop in at CenterMass Firearms for directions.
You are coming out one week too early - on Dec. 1st and 2nd we have a gun show AND Front Sight is offering their free subgun class. I will be at both!!
Either way - enjoy your stay here in Vegas and don't forget to gamble, it keeps my taxes low!