You could try this set
http://www.ebay.co.uk/itm/ALLOY-13T-14T-15T-MOTOR-PINION-GEAR-B-MINI-T-RC18T-RC18-/110688117008?pt=US_Character_Radio_Control_Toys&hash=item19c586a110&clk_rvr_id=756746933336&rmvSB=true
thats what i started with just keep the plastic spur, do you have a dual disk slipper in there???
links to mine
http://www.msuk-forum.co.uk/topic/161614-ecx-smash-need-parts-list-for-brushless-upgrade/?p=1621078