Where can I have my dragonfly R/C electric radio controlled helicopter serviced?

I have an older dragonfly 4 channel, electric powered, radio controlled, helicopter, I purchased it back in 2004. During my last crash the pinion gear came off the tail motor, and was lost, the motor however still works fine. I have prechased a new tail motor with pinion gear, it is for the new Walker Dragonfly model #4, not the older Dragonfly 4 channel helicopter that I have. It is longer, heavier, and the magnet is much more powerful, will the replacement motor work, on my older Dragonfly helicopter ? Or will I have to find a replacment pinion gear, for the original tail motor? If so where could a replacement pinion gear be found?Where can I have my dragonfly R/C electric radio controlled helicopter serviced?
Possibly radio shack.