I just used some 1 or 2 amp diodes straight from Radio Shack for the epoxy (round) diodes and something comparable in size for the smaller diodes from Radio Shack as well.  I don't actually own or have in my possession anymore the instruments of which I'd made the repair but the diodes didn't need to be anything special (fast acting, etc.), just needed to be able to handle the current loads.  I'd looked everywhere for exact replacements but could certainly not find anything like the epoxy diodes.  Technology has improved since the Matrix 6 was manufactured anyway...