There's a shop in Silverthorne that demos Mantras -- I think it is Pioneer Sports, but not sure. Virgin Island might also have them. AFAIK, there is no place to demo Mantra's at Copper itself.
If you are coming up from Boulder/Denver, Christy's in Boulder (184) or Denver West (reportedly) have Mantra's to demo. I demoed from Boulder -- and wound up with a pair that I did not need, but wanted (yes, I'm a gear whore).