I’m Denver proper as well. I have two mature peach trees that I’ve harvested for a number of years: an Elberta and Contender. When you say that
one makes the most delicious eating peaches ready in August
is it early or late August? If it’s early, my guess is it is the Redhaven. If it’s late, there a good chance it might be the Elberta; I harvested my Elberta this year on August 27th.
First, if you ever look at some the websites from Palisade, their peaches are all over the place, from some of the earliest windows to the latest. In my opinion, the only thing that really separates Palisade from the metro area is the yearly low temperatures (7a vs 5b), which allows them to grow less cold hardy peaches, as well as the slightly less frequent spring frosts. Otherwise we have the same dry climate with hot days and cool nights; as long as you can avoid late frosts and hail, I think Denver is a great area to grow peaches.
Though it’s an early September peach, I would generally recommend Contender. This year it ripened about 14 days after Elberta, though in prior years their window is closer together. It’s a good tasting peach that has hardy blooms for our late Spring frosts. That said, I have experienced winter die back on the tips on the years we get into the minus double digits. Reliance (which I have one of, though it’s young) is probably a good bet as well, though it’s in the same general harvest window as Elberta and Contender. If you want to extend your harvest, their are some other options out there, but I don’t have an personal input. Checking out some of Olpea’s peach observations might be beneficial.
As far as where to get your next tree, I might go against the grain in my recommendation, but I would go big box - assuming you come across one that has decent nursery tags for it’s type and doesn’t look too dicey. In Denver you can go to Home Depot or Lowes and find a pretty decent Contender or Reliance for a decent price. Sure, you won’t know the rootstock, but for peaches in Colorado and don’t think it’s as big a deal as other locations (peaches in the South) or fruit types (apples, for example).
If you want a nursery experience and are willing to go on a bit of a drive, I’ve gone to and recommend Holly Acres Nursery in Elizabeth when they have their bare root trees on sale in the Winter. Looks like this year they’ll be $30 bucks each. Otherwise, if you go the tradition metro-area nursery route, a place like Nick’s Garden Center, will have you paying $~250 for a more mature 3-4 year old tree - pretty standard for a lot of metro nurseries.