I have been buying hardy cacti from Desert Nursery for over 20 years. Plants are large and well-grown with an excellent variety to select from. Most of the hardy cacti listed do quite well in Colorado, where winter temperatures exceed -10f every winter and almost every night goes down into the low 20'sF every night from December through mid March.
This was one of the first nurseries that I dealt with when I wanted to start growing cold hardy cati & succulents. They have a very large selection of cacti, succelents, and agaves that are catagorized in their catalog from cold hardy to tender as well as point of origin for the exact stock that the plant for sale comes from. They are a pleasure to deal with, have great plants, and have excellent prices. Very high recommendation!!