There are wild hops in the Pine Valley Ranch open space in Jeffco, just north of the parking lot on the railroad trail. Both male and female, so watch out. I harvested some seeds a few years ago, but they did not germinate.
There are also hops on Plainview Road and 72, just west of 93. I was just out there, but did not look around. I have heard about Central City and Lyons, but have not checked them out.
The USDA did a hop collection survey and wrote a report. http://www.ars-grin.gov/cor/reprints/hopexpedition2002.pdf
it lists their collection sites.
Naturally, it is easier to get clippings from existing growers. I have Centennial, Cascade and Zeus; I would give clippings out next spring.