shtterman on ebay has them. NOS comes up on auction every now and then too. If it helps, the 29,35 & 40 Red Heads share the same backplate gasket. The cyl base and head gaskets are different. I think the 40 head and base gaskets are the same OUTSIDE diameter as the 35 gasket. You may be able to trim the INSIDE diameter on a 35 gasket to fit but it is really narrow and leaves little to zero room for error.