https://www.gohunt.com/

It will provide info on units. Draw odds, success rates, numbers of hunters (licenses), public land, etc. However, since your not trying to draw a tag, you can probably get most of what you need through the Colorado Parks and Wildlife website. Pick units with over the counter (OTC) licenses for the season you want to hunt.

http://cpw.state.co.us/thingstodo/Pages/BigGame.aspx

This mapping tool is pretty useful too.

https://ndismaps.nrel.colostate.edu/index.html?app=HuntingAtlas