I have a selection of fantastic looking machined aluminium control knobs for sale courtesy of one of the polygraphs seen in this thread:
https://www.eevblog.com/forum/other-blog-specific/huge-polygraph-lie-detector-machine-teardown/There are three types and three colours, all have a 1/4" shaft mounting so will also fit 6mm shafts and come with a retaining grub screw.
All are £1.50 each + worldwide postage at cost
Type A is a rectangular block shape measuring 12.6*12.6*22.1mm available in brushed silver, black or gold
Type B is a circular shape measuring 25.3 diameter by 14.3mm high, knurled area is 12.6mm diameter available in anodized black and gold
Type C is a square block shape measuring 18.9*12.6*12.6mm available in brushed silver only
Note there is some variation in the gold colour finish, if you want more than one of the gold i will try my best to match them!
Quantities available are:
Type A Silver: 18
Type A Black: 13
Type A Gold: 6
Type B Black: 6
Type B Gold: 21
Type C Silver: 4