Chuck,
So sorry to hear that. If you haven't already done so you should email Planet Bluegrass to see if it they have it in lost and found or perhaps they will check based on this posting.
You could also try contacting the town of Lyons to see if anyone turned it in - (303) 823-8250
recreation@townoflyons.com (that is the Parks and Rec dept. but if they don't do a lost and found they will get you to the right place.)
You could maybe try the Boulder County Sheriff and see if they can connect you to the Lyons office to see if someone turned it in there.
I think I'm going down to a concert tomorrow night in Sandstone park and I'll try to remember to stop in the visitors' center to see if anyone turned it in there.