You could ask Hank Wang. He can sell the bare Emisar D18 copper MCPCB which has 18 3535 led footprints for 10$, I think.
But those MCPCBs are all 3V while the L6 uses 6V with the long tube. Which kind of driver are you planning to use?
There is no spacer sold that I know about. I have made a copper spacer for my modified flashlight in this years Old lumens contest. The optics and MCPCB of the Mateminco MT18S fit perfectly in the L6. Here is my build thread: Matainvoy ML18S