Hello Serge,
20-inch tyres with the NATO tread pattern are often used on CMP trucks, see the picture of one
for sale in Holland. Personally I think they are perfectly acceptable as they are better than 70 year old tyres.
You could also check out other types available at
www.vrakking-tires.com (no connections), they have a wide variety of 20-inch tyres in stock.
Regards,
Hanno