Try www.moon-audio.com and also parts-express. That sould get you started. There is also Parts Connection and of course, "Rat"-Shack (if you are desperate).
And also: .......... How could any one of us forget to mention the CREEK OBH (passive remote pre-amp) series. I beleive that Moon Audio still has them and Audio Advisor sold them (at one time). They are quick to sell on Audiogon. Perhaps what would help you the most.
I scanned through the Audiogon website looking for something for you. There was (very recently) someone that was selling high quality switches and pots (under tweaks or ss pre-amps) but I could not locate anything now. I did happen to spot a "Quasar" switch box that looked real interesting but it is FAR more than you would need. What caught my eye about it was the (apparent) high quality of exposed parts. Fairly cheap at about 200.00. I don't know a thing about it's insides (could be pure junk). It had a ba-zillion in's and out's and for both amps and source. Made me dizzy looking at it.
Tubby