Penny & Giles (www.pennyandgiles.com) are best known for their line of "industrial" controllers and linear faders. They also make a rotary fader (model RF15) which is the volume control you are asking about. It is built like the proverbial tank and looks like it would withstand a nuclear blast. I used these in my Deluxe Line Drive series of passive preamps back in the '80's, but gave them up after I found a part I liked better - the TKD conductive plastic pot. Like Penny & Giles, TKD makes a line of industrial-grade linear faders, but they also make rotary faders (potentiometers) and stepped-attenuators. These are excellent volume controls, but the stepped parts have gotten extremely expensive. The conductive plastic pot (CP2511) can be had from Michael Percy Audio (www.percyaudio.com) for $62.50, while the stepped-attenuator goes for around $250.
Best regards,
Steve McCormack
www.SMcAudio.com