I used CD motor in a Hornby HST a while back. They fit near perfectly the only issue being getting the drive gear to fit snugly on the motor shaft.
They can be picked up easily from junked PC's, laptops or stereos, here's a link.
http://irishrailwaymodeller.com/showthread.php/77-Graham-s-Workbench?p=51957&viewfull=1#post51957