[Ron Ramirez]

Any known source for knobs?

Not really. They are highly sought after, and the prices range from very high to ridiculous. I've never asked Mike Koste if he has any Fisher knobs; I need to. I have a circa 1961 500-S that is missing some knobs; they are different than your 500-C knobs and appear to be much harder to find.

This is probably why your 500-C that you bought from the auction site was missing all of its knobs. There's gold in them thar knobs! And the missing tubes - 12AX7 prices are crazy, just crazy. 12AT7 prices aren't far behind. And these are not rare tubes! Not to mention the 7591A outputs...

Just recently I purchased a Fisher Ambassador tuner, a pull from a console. The seller included a bag with all of the knobs! That wasn't even mentioned in the auction ad. Great bonus! I hope to eventually own an 800-B and *maybe* a 500-C or 800-C; if I end up with one which has missing knobs, I'm pretty well set now. Or I could use them as (incorrect) replacements on my 500-S...