Here's the closest match I could find: http://www.mouser.com/Search/Refine....3F0GHSY00D0244
This potentiometer is made by Vishay, and is the P11 series. Full specs here: http://www.vishay.com/docs/51031/p11.pdf
Product code: P11A3F0GHSY00D0244
I figured out most of the bits in the ordering code EXCEPT the "D0244" suffix, which didn't seem to mean anything. However, Mouser claims this means a 50K resistance with 10% tolerance.
The "F" means that it has a standard 3/8" diameter bushing with 3/8" length. This means it should fit into the electronics cavity of most solid-body basses, assuming your body thickness isn't more than 1/4" inside the cavity. Of course this would also work fine with a pickguard. The "GHS" means that it has a solid shaft of 1/4" diameter and 3/4" total length - subtract the length of the bushing, and this means that you have a good 3/8" of shaft to which a standard metal knob (for 1/4" diameter, not 6mm) can be attached. The "Y00" means it has solder lugs approx 0.200" apart.
It looks like this is actually a triple-ganged pot, but you can just ignore one of the sets of pins and use it as a dual-ganged pot.
The bad news is that these pots are only orderable in quantities of 25, and cost $15.31 each.
I've checked other distributors (Newark, Digikey) and didn't find anything close to this in stock. I haven't gone to the trouble of asking for a special order.
So, does anyone have a spare $382.75 lying around to purchase 25 of these pots and test them out? I'd probably buy a single one for $20 if it works.