Did a quick search on the internet for
tc3 trasmission aluminum and found the item you are looking for made by RD Logics (
http://rdlogics.3dcartstores.com/Par...tc3_p_406.html)
It appears that Horizon Hobby used to sell that part, but it shows as out of stock (
http://search.horizonhobby.com/index...d=1311EDF4C136).
Hope this information helps.
I should note that the Electric TC3/TC4 and Nitro TC3 all use the same diff cases.