Simple question: what can you graft to purple leaf sand cherry?
If anything, you can try plums.
And i would have to assume that they would last the usual 10 or so years sandcherries seem to live as well. Sandcherries can also pollinate some plums as well?
Prunus besseyi used to be a standard dwarfing stock used for peaches, plums, and cherries. It doesn't perform super well so its not so common anymore. I have a 10-year plum on besseyi that still seems to be doing OK. It has severely overgrown the stock (I forget the name of the condition, when the rootstock is half the diameter of the scion on top of it) but the tree is still looking healthy.
What scott said.
I've not used P.besseyi, but have played around, in the past, with some P.americana and P.tomentosa(Nanking cherry - which is actually more closely related to plums than to real cherries) - plums and peaches worked OK on both understocks - Nanking dwarfed peaches very much.
Purple Leaf Sand Cherry, [Prunus x cistena] is not commonly used,...just experiment.
Western Sand Cherry, [ Prunus besseyi ] is a good pollinator for cherry plums.
I hand pollinated these,..about 90% more productive.