I said I'd drop a line to you all if suitable motors became available on
EBAY ... and these may be good for stepper mice. I think they're 28mm, which
keeps the weight down - and they are cheap (probably even if shipped to
UK).
These are 6 volt, 0.8 amp, 1.8 degree/ step.
Model is PX245-028-C8, manufactured by Oriental Motor Co, LTD. JAPAN
Tony