Ion Petroianu, VA3NOI
I‘ve bought knobs from Tayda Electronics.
I also changed the volume pot with one that has a regular, 025" dia shaft, without switch.
I use a DPDT ON-OFF-ON switch to turn ON/OFF and switch the power to the PA from 12V to 20V.
You can buy the knobs you like from Digikey. Delivery in 24 hours.