The first thing you need is a metric ruler. If you of course can not find a model number on the motor that you have. If it is round you will need 4 measurements. The shaft length and diameter, the body length and diameter. If it is a squashed can you will need the second diameter as well. Then you can shop via the faulhaber, maxon, portscap, mabuchi, etc website. Find a motor that fits the size. Then I recommend getting it in 12v as those are more. Compatible with more power supplies. Once you have the model number, punch it in google or eBay. Good luck