Unfortunately the 36V chips are alote more popular and more readily available.
KingBrite is the place you want to go to get your Cree COBs
Here's the link -
https://kingbriteled.en.alibaba.com...XB3590_3500K_CD_CXB3590_0000_000R0HCD35G.html
they do both 36v and 72v versions.
I'm much more in favor of the 36v version but i can see why people want to go the 72v route.
My CXB3590 is a 36v and can be seen in my journal. It is only a single chip light due to the fact it is in a PC micro cab.
I will be building some more CXB3590 COB lights in the autumn with a full how to build tutorial.