I have just purchased a couple of switched pots from this Ebay supplier.
http://harrisonelectronics.co.uk/
They do quite a range of single, dual and switched pots with log and linear tracks. Unfortunately they don't appear to do 500k (470K) or 1meg switched log pots (at least at the moment) which are values we commonly require.
The pots have 1/4 inch
round shafts (not standard flat) which are 55mm (2.17 inches) long. They use the standard fixing thread, so if you loose the nut, the one off the old pot will fit. The shaft is plastic, not metal, but that can be an advantage giving extra safety in live chassis sets.
I paid £1.75 each for my 2 switched pots plus £1 postage. Although that is cheap the quality looks quite good but only time will tell for sure.
Colin M