Any of the late bloomers (which are the U of Sask and Maxine Thompason varieties) should pollinize each other. Honeyberryusa has plenty of info.
I enjoyed all 4 that I planted. Keiko was the most unique. Beauty the best rounded and rivaled a great blueberry imo. They need to hang after turning blue for a while to get the best flavor.
On another note I had a bad time with alnifolia serviceberries. I think I planted Regent. It got itās butt kicked in August by my Piedmont summer. Iād probably try the Allegheny if I had more space.
Jury is still out on black currants at my location.
Try the hybrids āamelanchier x grandifloraā such as Princess Diana or Autumn Brilliance or even a un-named āapple serviceberryā. The ALNIFOLIA donāt work in zone 6 much either!