Here is a link to a Panzer III one of our club members made battle ready. He kept the stock metal drives, and got the Tamiya Electronics off of E-Bay. Depending on how many parts you need, buying the whole tank and parting out what you don't use might make sense.

http://web.mac.com/ksoc/Special_Proj...zer_III.html#0

The American Armoured Foundation Tank Museum (Danville) is good source for all Tamiya parts and kits. Look on the PX page for more info

http://www.aaftankmuseum.com