I heard that someone put on a different spur from a nitro team durango something like a 47t....i don't know if this is nonsense or not but you could have a look.
Intigy makes some spurs for the HPI C1/Apache that fit, sort of. You get a bit of out drive play because of the 6mm bore vs the Arrma 5mm bore. These spurs come is sizes from 48t down to 38t.