the HPC catalogue is a good referance but its cheaper to buy from RS or Technobots. See if you can get hold of a couple of old 24v Golds and use their front plates instead of the ones fitted on the 12v ones. Are you running the 12Vs at 24v? Alpha uses MOD1 steel gears, probably abit OTT but theyre the smallest i could get hold of, i could turn them down...but that requires time :P