I rang my local Kwik-Fit branch and like some others who have posted here they said they didn't have any Winter tyres in my vehicle's size (175/65 14).
However, while they didn't seem to have any idea as to what stock is held at their central depot/warehouse (they admitted as much) they recommended that I look online at their website where in the end I was able to buy Continental tyres similar to the ones in Jon's article and have them fitted wherever.
Seems a strange system as if I hadn't persevered I would have been left with the answer that they didnt have any tyres "full stop".
Thanks for that Paddy, I am now re-assured. Perhaps we will start at the western side and work east doing any detours along the way and then just see. Which is the days stretch which is still under negotiation? From where to where? I'll do without a tent if I can. At the moment I plan on going in mid-September and so sadly I will miss out on your new guide, "Walking in Mallorca", which Cicerone tell me is due from the printers at a date slightly after my departure. I think in the meantime I will get some maps...