A very high quality- full size ALPHA brand 500k volume pot- Audio taper for use as a volume pot- Real high Quality Potentiometers
, smooth as silk, reliable as heck, solders like a champ. I've used about a bazillion of these over the past few years and find them to be far preferable to the "mystery" 500k pots sold by a certain well known importer.
These are split shaft but will work both with push on knobs and knobs with a setscrew.