There is an open source implementation of the SuperH instruction set: http://j-core.org/index.htmlBootlegs/repro's/something would make a lot more sense than a multi. SH3 CPU's got discontinued, and finding them in large quantities isn't terribly easy.
They implement SH-2 and some SH-3 instructions that are not covered by patents, though I have no idea if it is possible to reach the required performance of the 133Mhz SH-3 on an FPGA board.