I notice that whereas you want a 50mm long shaft Tony, those on e-bay have only a 44mm shaft, though I guess might do. (Also, there are two in the pack).
I’m probably too late to say that pots with 50mm long shafts are available from Bowood Electronics, who some forum members might be familiar with. (Bowood was established some years ago by Wilf and his wife Jan. He's great guy who used to work for Bardwell’s in Sheffield). I recently needed a 1 meg switched log pot and they're not so easily come by, but Wilf stocks them. He also stocks 470k (as needed for the DAC90A etc, and 2 Meg, as well as lower values, and linear pots, and stocks un-switched pots too:
They're nice and compact, which I was pleased about as space is very limited in a Dynatron record player that I'm restoring, in which the switch on the pot was duff. The one supplied by Bowood was identical in size. Often the plastic shafts are quite ‘bendy’ but these are quite stiff, so make a good replacement for metal-shafted pots.
I assume that the pot you are looking for is for the volume control and hence, needs to be log law, but if it is a tone control would need to be linear. Bowood sell both. Here is the link to the 10K ones you are after - log and linear tracks:
http://www.bowood-electronics.co.uk/...switched-p-652
http://www.bowood-electronics.co.uk/...switched-p-651
£2.45 eac + £2.85 p&p
Wilf sells lots of other useful stuff and post is modest, as are his prices. Service is speedy too - my pot arrived next day.
(No connection with Bowood, other than as a long term satisfied customer).
Hope that helps - if not now, in the future or to someone else.