Stereo system has pair of speakers in four locations: fwd cabin, salon, aft cabin and on the arch. Volume for each pair independently controlled by a double gang rheostat (potentiometer) rated at 8ohm, 30watts. Since a couple of these have become nonfunctional I'd like to replace them. Can't find a product like this anywhere--tried the internet and electronics stores like Fry's and Radio Shack. People there ask "what's that" and thus ends the conversation. Anybody have any ideas where I can find this type of volume control or maybe a substitute that will work?Thanks,Bruce