bj, I'll bet dollars to donuts it's out there, but it is hard to find. Around here it likes shrubland and transitions into thicker woods where there's small pools of standing water. It grows between the pools.
Ed, that KCT bow sounds like money in the bank. That's another wood I've always wanted to try, but certainly will never find up here so... I'll look for some more plum and you look for the KCT and... you get the picture.
One thing about plum is it does check like crazy and while it was drying a crack developed lengthwise on the handle which lead to that handle-wood popping clear off during tillering. So I just glued it right back on and wrapped with sinew. No other wood added. As for the no set, yeah I did okay with the tillering but I think plum's so good in compression that I really can't take that much credit. Others have said they got almost no set with plum either.