I just got back from Denver and Boulder (so nice!) and signed Columbine copies at Denver's Tattered Cover on Colfax, and the Westminster Barnes & Noble.
(I went to Tattered Cover's LoDo store, too, but they were out, or hidden somewhere. Inventory showed two, but none on the shelf.)
More info and pix coming.
Info here on ordering autographed Columbine copies. (The NYC B&N has the most copies and your best bet if you're ordering from afar.)
I'm really sorry I didn't get to the Boulder Bookstore, or the B&N in Boulder. I was planning to, but dinner ran late the night before my plane, and of course I left late for the airport. Oh well. It was a short trip, and so much to do. I'll definitely hit them next time.
Update: Back in NYC, I signed at the B&N UWS (82nd and Broadway) June 1.