Lots and lots of public land west of Denver, and a little bit east of Denver. To gain access on private land east of Denver for antelope, and even mule deer, can be a little tough, BUT what I've learned is that if you get far enough east and take the time to knock on some doors, be curtious, and ask for permission, it's really not that difficult to get access to private property.
Here's my best secret for gaining access,coyote hunting. It's very easy to approach the farmers and ranchers AFTER all the other seasons are over and ask to hunt coyotes. Once I gain access to call coyotes, I use that to get to know the farmers and it gives them a chance to get to know me, and if I see that there's other good hunting game numbers on the land, I will eventually, after a year or two, ask permission to hunt other animals. This has worked well for me over the last 20 years, I now have more private land to hunt than I can cover in a winter.