The Airfix ones used to be spin to start and can be run from a one cell battery (1.5 volts). The shaft is offset from centre. You stop them by just stopping the prop with your finger, and they don't take any power until you spin the prop again to start them. I have dozens of them in my workshop so if you want any just PM me.
If you want a bit smaller try this site, they start at 4mm diameter.
http://www.precisionmicrodrives.com/...9fd9b6513c258b