i know got them on eBay they are second hand wheelchair motors need them for my end of year project at uni found a controller while searching teh internet
http://www.trossenrobotics.com/store/p/5106-Sabertooth-dual-10A-motor-driver-for...
would this one be what i was looking for.
This one can only handle 8A at 24V, wouldn't be enough for you.
When you find your external battery power source, keep in mind, output voltage of a charged battery can be higher than the rated voltage. e.g. a 24V battery when it's fully charge might output as high as 28V or even higher. I suggest to get a driver that can handle higher voltage than 24.
or i found one at spark fun
Motor Driver 15A IRF7862PBF - ROB-09107 - SparkFun Electronics
this driver is rated for 18V batteries, and can safely handle maximum of 24V so wouldn't be enough for a 24V battery.
This one would be good for 24V battery, since it can handle up to 34V and does 12A continuous:
if you need something with higher current than 12, use this one
operates safe up to 34V and can do 20A continuous.