i have a 1/10 rc petrol car and need a Spur gear for it but the car has no name on it anywhere ?

It has a BMW shell in silver and the front shocks are yellow the back are blue.
The spur gear has 43 teeth

Joshua,

you're going to need photographs - the shell and the springs are two of the most easily changed things so you'll not identify the car using them.

Does the engine have any names / lettering stamped on it to give you a clue - otherwise if you're using the original radio have a look for branding on the reciever / servos.

Failing that, take it into a local hobby shop and let someone in the trade take a look and see if they know what it is.