J Bull Electrical in England used to sell "Big Trak Gearboxes", the little plastic gearboxes with two motors, for a few pounds for *years*. For all I know they still do. Their website is as full of bizarre stuff as their magazine ads used to be - from random bags of components to Sinclair C5 motors to the aforementioned gearboxes to Chinese Army air rifles which were so powerful you needed a firearms cert for them even back in the comparatively lax 1980s!
I'm glad to see they're still on the go. Their adverts in Wireless World and Television were a great source of wonder for my geeky friends and I when I was at school some 30-odd years ago, and finding they're still as batshit as ever has cheered me up no end.
Now I wonder if Display Electronics ever shifted those 9" bare chassis Microvitec colour monitors from National Air Traffic Control, or indeed their deactivated heat-seeking missiles?