http://www.rubberstation.com/Mm2(English).htm
is a list of tyre companies that I found, if anyone has the time/inclination to check them. I have also made an enquiry as I cannot believe, in my capacity as a military historian, that the War Office laid down tyre specs and yet now those tyres canot be found or are unsafe, overpriced or wrong tread pattern. I will do all I can to assist here because I used to have business contacts in the dim and distant past.