I'm trying to get hold of a 12V motor with a gearbox to provide around 500 rpm and a decent amount of torque. Plus the speed control mech.

Something like golf trolley, wheelchair, kids toys DC motors.

Its for a project I'm working on.

edit - sorry if its a bit cheeky sticking this here but I'm running short of ideas and don't want to spend loads.

 

Starter Motors are pretty torquey - no idea on the gear box side

 

Not sure how many RPM this is, but you could change the gearing with a chain and a couple of sprockets perhaps?

eBay.co.uk: Golf 12v motors for eletric golf trolleys (item 220052576193 end time 30-Nov-06 13:56:34 GMT)

 

Check RS COMPONENTS & FARNELL, google for websites.

High torque with good speed control, see STEPPER MOTORS

 

try 'robot wars' ubergeek forums. Thats what they use.