There was plans at one point to make a 7 up Metal Core PCB for the Cree XRE, but, it has not gone anywhere.
Instead, there is the thin PCB flower for the Rebel which is a smaller footprint and when coupled with the 10mm Rebel refector will fit in smaller heads. The width across the the array is only ~1.2". Lots of clearance in the Mag which measures close to 2" across.
I have not seen any sales on the thin PCBs. Don't know why. They enable you to mount the Rebel on something small and have great thermal management. Thin PCBs can be shaped with scissors.
The Rebel thin PCB 7 up can be cut to create a tri-cluster and that is what I did to make two tri-heads for my soldering station lighting.
You can see the full thin pcb in the background and the cut up version in front of it in the picture below.