The tyre valves are defiantly order able from different sources other than ford. The valves should be changed according to manufacturers specs every time you change a wheel, but. It isn't the valves that are at fault, it is the corrosion around the valve.
1.6 tdci, remapped to 120 bhp, Panther Black Titanium with rear view camera, nav pac and front sensors. Always willing to stop & help in any situation I can. Karma is a beautiful thing.