Thanks for all the comments so far. I recently purchased both ARC's used, and had both serviced by an authorized dealer. All tubes measred well, and bias settings are correct and have barely drifted since acquiring the amp.
The original pots are from Alps and not longer available. I'd try finding Japan sources. Do you, tomic601, have more information on that or Fleaboy?
I should state that I am thrilled with the sound quality of my ARC gear.