The best I've found in Las Vegas Nevada, is Record City, 300 E Sahara Ave. They have nice a selection of collector and rare lp's. It is located close to the "Strip" in a "not so great neighborhood" and looks like a dump but it's well worth the time. There are a few others in town but just don't the inventory and quality product. The same owners have another store located a few blocks east with less inventory and a little better prices. they are not open Sundays.
Good luck.