Whenever I'm in Vegas I head to Master Shooter's Supply. But then again I'm biased - my best friend works there on the weekends!
They're located at: 4017 W. Sahara Ave.
I asked and he said they don't have any mini-14 mags in stock right now - everyone is asking for them - but you never know.
It's a good family-owned shop and I'm sure they won't steer you wrong on prices.
Devin