Well, I don't know the area since I'm from Florida, but I did a hobbyshop search here https://www.hobbyretailer.com/ and came up with a few results. I know HobbyTownUSA sell rocketry products and they came up as one of the results. Also, you might want to try Emailing someone from https://www.tripolivegas.com/. I bet they know of the best spots. If I were you, I'd be sure to find out if there was a HobbyLobby nearby. That dang place seems to be giving away rockets. You might score some good deals there if they have a location nearby.
I'm positive someone here local to the area might respond.
So let me get this straight - you're going to be on vacation and you're gonna go rocketry shopping? I suppose I'd do the same if I were in another town!
What's wrong with that? I'm going to Hawaii for Christmas and *I'm* going to be playing with rockets! (I know - Vegas is a "playing/gambling" state...) I plan on scouring whatever local hobbyshops are over there just to see if I can find me some good deals. There don't seem to be any rocketeers in Hawaii (as far as I know), so there might be some OOP stuff just sitting on shelves. And yes, rocketry does exist in Hawaii. I believe there's an NAR chapter over there.