I would recommend going to lvcva.com (Las Vegas Convention and Visitors Authority) and navigating through the menus until you hit their 90-day event calendar. There is a "shows" subcategory. The info there is pretty up to date and accurate.
LiveFreeNW recommended visitlasvegas com, and I do as well, though they are one of those tiresomely ubiquitous websites that try to sell you stuff and sign up for this and that before they dispense information.
The good thing about lvcva is that they don't try to sell you anything. One thing I'm finding tiresome about the interblab is that you can't look up how to spell "cat" without somebody trying to sell you a dictionary.
LVA does have upcoming shows info in their newsletter.