REI is probably your best bet. It's on Hwy 36 in Boulder on the way to Lyons, so convenient. (The big flagship REI store is in downtown Denver, if you're coming through Denver). I have the wooden Byers chairs, they're great. The thermarest padded foldup chairs are pretty comfortable, lightweight and convenient. I would call the Boulder store in advance to check availability. You may be able to order online and have them hold the chairs for you. They Byers they might have to order in advance so contact them now. Go to
www.rei.com and search for chairs.
As for donating them afterwards, I'm sure you could find some local festivarians that would love to take them off your hands!
-Rob