Gotta get age verified, and that takes anywhere from a few days to a couple weeks. That and there is the problem of finding the guns itself. You also have to be 18 years of age, or older. You're also looking at spending atleast 300 dollars for an individual pistol.
So, sorry to say, you're out of luck.
(Also... Taking very REALISTIC replicas to conventions can be pretty sketchy, I'd just make them out of cardboard or something. Get creative. Its cheaper.)