I usually go to Cycle Gear on 344 S Decatur Blvd, Las Vegas, NV - (702) 877-4327
Store Hours: Mon-Thu 9-7
Fri 9-8
Sat 9-7
Sun 10-5
www.cyclegear.com
They have a wide selection and they are open late. They have specials all the time, so you might be able to catch one. In my experience their prices are always a little better than the actual bike shops. They also have a second location in Henderson, but that is a much smaller shop with a limited selection. If you can't find what you are looking for at the big store, they can always call the other one to check if they have it.
I hope this helps,
AJ