Vegas is easy and cheap to get to. The Antique Arms show is a decent show that will give you probably the best chance to find what you are looking for. But as you know it will be hit or miss. Heck the gun shop down the road might have what you are looking for but the chances are extremely small. What Vegas does is concentrate several best chance dealers in one spot. You might go and find three of what you are after or go three times to find one.
The other thing is that like Tulsa or Louisville show it is hard to see everything. Easier to network with someone else who is at the show and go different directions. Use to do this with a friend who was interested in pre war II custom Springfield or Krags. If I found a decent one I'd call him, it he found a Lefever 20 ga. C grade or better he would call me. Still waiting for that call.
