.
Extract them from the ROM, you mean? The only way I know of would be to open your ROM in a hex editor, look for an "INIT" string, write down the address it starts at, and tell the snes9x debugger to disassemble from that address. It might be difficult to tell where the code ends and what sprite you're disassembling, though.
What custom sprites do you have anyway? If you haven't coded them yourself, they must still be around, so why not re-downlaod them?