Have you check the Fashion Mall on the Strip, if they are open - I know that there's a few mobile phone kiosk, including authorized T-Mo counters/agents and they should have something.

Likewise, if the Walmart over at Rainbow Blvd/Maryland Pkwy - head west crossing over I-95 on Spring Mountain Rd, google for the Best Buy - closed now & should be open by midnight (10 pm for Walmart) for Black Friday - you might want to buy the cheapest throwaway prepaid phone as it comes with a SIM card, ready for activation.

Otherwise, you will have to wait till tomorrow ....