You can use a tdr colleted adapter and run the thread on gears Mike sells in the rcm store, use the 2nd speed gears.
You can also use the 2 speed adapter that mike sells, but you may have issues with the gear unthreading when you brake or reverse.
Go to sdp-si and try to get something that will work. Stainless will be your best bet, but you will have to use the plastic 63t spur as those gears are not hardened.
Only thing sdp-si has in stainless mod1 with 5mm bore and set screw is 30t, then 36t. Not sure if a 30 will work for you. The tdr colleted adapter and Mikes hardened gears is about the only game in town over 25t... I have had good success with the 25t pinion and 63t spur. If you want more speed you can always go with taller tires! Losi also makes a tin coated 59t spur, but you may have issues getting close enough mesh with the tdr mount.