One would think there would be some kind of website or publication where all of the landowners posted whether they were willing to allow hunters and how much they charged for a trespass fee.
One might think that but, in the real world, it's up to you to do some research. If I were you, I would start by subscribing to exbiologist's westernhuntingdata.com to learn about where there are the best opportunities for tags and hunts. If you specifically are interested in private land tags, look at the units where they are available and get to work on your computer and your phone.
Most towns in Colorado in areas with good big game populations have Chambers of Commerce that maintain lists of local landowners that may be looking for hunters. If that doesn't work, get on Dexknows.com and find out the name and contact information for local sporting goods stores, archery stores, etc., and call them to see if they know of locals who will accommodate private land hunters.
Even better, once you have identified a unit that seems likely, take a few days or a week before the application deadline and visit and talk to the locals in the chamber, the sporting goods stores and the gun and archery clubs. If you get some names, contact the ranchers or landowners and visit with them to determine if their place is somewhere that you might want to (and can afford to) hunt.
I do know folks who have scouting services for New Mexico and adjacent states and their services are worth the money if you draw a public land tag, but it will cost you for the information. The only way to find out for free (or relatively little in the case of westernhuntingdata) is to spend the time doing the research. BTW, I have no financial or personal interest in Mark's information service, but there is nothing else that I know of out there for the price.