Hi Chris, 
I apologize for not getting back to you sooner! 
We do host a tree sale through the CSU nursery, Here is the page with the order form. 
http://park.extension.colostate.edu/seedling-guides-and-order-form/
The order form has markings on the trees that are good for Park County - Those ones are a range from 8,000-11,000 feet elevation so if you see one that you are interested in check this guide to see what the recommended elevation is - https://park.extension.colostate.edu/wp-content/uploads/sites/51/2018/11/Trees-Buyers-Guide.pdf

For planting and forgetting... that is a bit harder. A lot of those trees above are pretty drought tolerant so that would be good however, that is once they are established. 
A few things that we recommend for people who aren't able to water as often is to utilize polymer crystals that absorb the water and hold it by the roots longer and then mulching around the trees to prevent evaporation as much as possible. How often would you say you would be able to water them? Could you set up a drip system with a large storage tank that you fill up when you are in town? Could maybe set it on a timer? Is there a neighbor who could check on them? 
Please let me know if there are additional resources that I can help with! 
Thanks,
Barbie