No clue about Denver, but I'll say that I've found some really good buys in pawn shops. Rather than knowing when they have something good, I've found that most pawn brokers (at least near Charleston, SC) are idiots when it comes to guns. Usually their prices make no sense - heck I saw a Nagan 1895 revolver in one for $495 the other day.
However, that incompetence in setting a price sometimes works in your favor. They often just don't know how to price a gun right, and sometimes they'll just set it too low.
Deals I've gotten recently (all within the last 2 or 3 years):
Like new conditions Winchester 670 in .225 Winchester for $225
Custom 1903 Springfield sporter with exhibition grade stock and hand-cut checkering $275
Good condition Marlin 336 .30-30 $165
Good condition Savage 340 .30-30 $99
Passed up a Mossberg 810 in .243 that they told me they'd let go for $145. Wanted to read up on it first as I'd never heard of it, and it was gone when I back back the next day.
Main thing though is to visit often. The pawn shop in the town where I work I visit 2 or 3 times per week. I check several others each weekend when I'm out and about. 99% of the time there's nothing of value, but if you check often enough you find some deals eventually.