Q.Can You Grow A Cherry Plum Tree In Mesa, AZ?
If so, where can I purchase one?

Certified GKH Gardening Expert
You are in zone 9b, which is not exactly the right zone for growing a cherry plum, however, you should be able to grow one if you can give it some heat protection in the summer.
https://www.gardeningknowhow.com/ornamental/trees/cherry-plum/cherry-plum-information.htm
As to where you can purchase one, Gardening Know How is a publisher of gardening info and we don't make retail recommendations. However, your local garden center should be able to order one of these trees for you, or perhaps you can find one online.