Starks says any Japanese plum will do. I haven't tried one, but they sound interesting.

It flowers like neither parent, totally covered with huge clusters of tiny tiny white flowers. I wonder if that's what makes it so hard to set fruit.

I have a Spring Satin and meant to graft a plum to it for pollination, but haven't gotten around to that yet, so there were no Asian plums around last year for the two blossoms it produced. We did have beach plums and apricots blooming at the same time, though. Both blossoms set fruit, one dropped early in the summer, but the one that finally ripened was delicious. It was also only slightly larger than a cherry and ripened very late so I'm not sure whether one of my trees cross-pollinated it, or if it's a case of being able to produce tiny fruit on its own.
I don't care for asian plums, so was hoping to find someone who would say an apricot was good enough. Everyone in the US seemed to agree it had to be a plum, but this place in Australia says apricot is fine, IF it blooms at the same time, suggesting that bloom time is what makes a plum preferable. http://www.plantnet.com.au/new-spring-satin-plumcot/

christy - I'd trust that site more if it didn't say SS was "partially self-fertile". I've never heard of an interspecific that was.

My Spring Satin also produced small fruit the first couple of fruiting years. They were not all that flavorful so I almost pulled the tree out. I am glad I didn't as it now produces very large plums with excellent flavor (as long as I thin enough).

Scott

Yes, as a general rule any Prunus species will cross pollinate another if their blooms overlap and they receive an insect visit. Identical species may have better success however. In the case of SS it is a hybrid. Interestingly SS will set fruit in Phoenix AZ. One of my pleasant experimental surprises.