Blender:
I sure did. Here's an Ebay listing with 5mm, 4mm, 3mm, and 2mm drive shafts - but they call them "steering shafts".
Drive shafts
The LDRC Unimog twin motor/gearbox that I'm using has 4mm output shafts, the WPL motor gearbox that I originally planed on using had 3mm output shafts. Since all of my axles have 5mm input shafts, I thought the WPL gearbox might have been a little on the wimpy side.
Don