I got a new clutch cable a few months ago from a Fiat 500 specialist, Nathan Robertson at Fiat 500 Classic (and also a choke cable). Prior to that I'd shopped around for the best price and from memory found about 6 different suppliers in the UK, and of course there are others in Europe like Axel Gerstl. I didn't get the impression that there was any problem with the supply of this or other control cables for the 126 models. It seems from all the different web sites that most differences are at the cable ends (as opposed to length or diameter etc) and there are many ways of adapting a coupling and of gripping a cable that are perfectly good engineering to get something to fit the situation. Fiat seem to have used a plethora of cable ends/nipples/split pins/plastic snap-on clips/ferrules and so on even within a single model when a single type would be perfectly adequate for all of them, with obviously a more heavy duty option for the clutch.