Lex, This is sort of what I had in mind. It's an easy thing to make up. Just get 2 FLAT SIDED spur gears the same size, or file/machine flat. Pref. plastic, (D.Smiths, JAYCAR), & a bit of thin felt? as the friction material. Thread your shaft at one end for the nut...........etc etc. HTH.
L.
ps. Not sure but, do the gears have a 'metal boss' with a grub screw for fixing to the shaft, or are they a 'press fit'? If a press fit, you might have to '
supa glue' them.