Finding 2 ply tires, Ag or otherwise, is not easy. Case, Deere, IH and other such companies were all giants in there day that produced a large number of products that needed tires. That fact put them in the driver's seat with Goodyear, Firestone and other tire manufacturers who were happy to make five thousand pair of 8:00 x 16 2 ply ag tires in a single order. However, when you look beyond the garden tractor industry, there were almost no other applications for a 2 ply Ag tire and that's the problem today. The demand for a 2 ply tire is nearly non-existent. No tire company is willing to do a large production run of 2 ply tires and then warehouse those tires for the next 5 to 10 years while they get sold off.
Demand for 4 ply and 6 ply 8:00 x 16's is much higher because these are OEM on the front axles of 4 wheel drive tractors and the greater number of plies are needed due to the weight the tire carcass is expected to support. For the purposes of restoration, the number of plies is of no real consequence unless you intend to parade the tractor on paved streets. Ride is the main issue but ag tires were meant for the fields not the roads. The document in the FAQ's provides a substantial number of URL's for people in the tire business. That's the best this site can do because tire inventory is something that changes day to day. You have to call these people directly and check to see if they have what you want in stock or if they can get it right now from their supplier.
Of course, you are free to ask about this issue on MTF, the Yahoo forum, GT Talk, Tractorbynet and other sites to see if someone there has a KNOWN source.