Bart Trzynadlowski made a SH-2 disassembler, and there's at least one more at Eidolon's Inn. Objcopy from the GNU binutils can also disassemble binaries. If you have the money, the full version of IDA Pro supports SuperH CPUs. This is the best alternative, but it's also expensive.
As for turning a binary to C source, forget it. I have seen one or two research projects, but they only worked for a particular version of a particular compiler (and were also x86-specific). Generally, it can't be done.