Howdy!
It didn't happen. There is no NCOWS in Las Vegas, NV, and given the nature of the shooters out here, there will not be in the foreseable future.
If you want to go to a local shoot with period correct attire, gunleather, firearms, calibers, powder, etc, you are more than welcome to. No one will complain. You will, of course, be way over dressed compared to the local shooters, and some will probably think you're not very smart for doing it, as they'll be thinking it will seriously cut into your ability to compete and win with all that stuff on while shooting real Old West calibers with serious loads. (After all, aren't we all there specifically to win?)
Ask me how I know this...