Plums, peaches, and apricots are not good pollinators for each other. True they have been crossed but it's not as simple as planting them next to each other or even pollinating by hand. Those crosses between species require special techniques.

You'll do better getting another plum to pollinate your Santa Rosa.

Methely or Shiro, I suggest. Your Santa Rosa may be short lived there- It is a relatively weak tree in my z6. Both Methely and Shiro have never shown any cambium problems from excessive cold here. Just a bicycle ride down south of me SR does fine. I'm on the cusp.