Yes thanks, I had found the eBay traders.
Whilst I am tempted to do it with proper parts, my 746 phone still has at least the original grommet, unoccupied, that I think I can bodge/modify for whatever old lead I can find. It won't be as neat as a new lead with correct colours, spade terminals and moulded grommet, but will be better than nothing - at least until I satisfy myself the phone, bell and handset all work.