Popper252

Hey man welcome to the forums, sucks that it had to be under these circumastance though. Do you know why it took off on ya like that? Did you have your radio and reciever turned on and working? Just instinctively before I go to start my car I'll pull on the throttle trigger and turn the wheels to make sure things are working right. You should try and make that a habit. Topspeed has all of the engine parts that you'll need and he's a really reliable guy. You won't go wrong dealing with him. Hopefully you'll get the parts that you need and you'll be up and running real soon.
And just as a little tip, be sure to thread lock the screws on your back plate when you're putting everything back together. They tend to wiggle out real easily. And while you're at it you should probably go through and thread lock as many screws as you can. Especially the metal to metal ones. It'll save you a ton of trouble later on.
The reason you're gear stripped like that was because you didn't line up the gear mesh properly. That'll cause it to eat right through the thing. Next time be sure to line them a little closer. I haven't had much luck with any of my gears so I can't give you much advice in that dept, but if you read through some of the threads you'll find lots of good explanations and ways to do it.
Good luck man.