Just for the record, the "special" tyre valves that the fitters make so much fuss about (one tyre firm said he'd have to get them from a specialist who delivers once a month. Yeah right!) aren't very special at all. They are TR415 and readily available. Widely used on tractors and old landrovers. 25p each for premium quality UK stock on eBay.
So I had to buy two new tyres, and the best quote was from the same place as last time. (I made sure they got the valves too)
When I took the wheels in I asked them to look at the code date on the new tyres. One was 2916 (week 29 2016) and the other was 0914 (week 9 2014). So I rejected the 0914 and they rang another depot who had another 2916 in stock. They swapped tyres, and I've now got two 2916s. As I'm unlikely to wear them out, and they are likely to be replaced due to age, that's two and a bit more years before replacement. The moral of that is "he who doesn't ask doesn't get" They love me in there!