try
www.technobotsonline.com
they are a UK supplier based in Hampshire
look under 'motors' - they stock Pololu motors plus the biggest range I can find for motors and gearmotors generally....covering all voltage ranges, from 3v up to 12v. You are certain to find something to replace what you have, or even upgrade.
Despite being in Australia, I order from them. First class service, they normally post same or next day