The only places I have seen serial numbers is on the bill of sale or in the repair/owners manual.
You have no idea where they went? Tractors usually need to be loaded on a trailer or flat bed truck.
We had an Allis Chalmmer B that my father gave to another farmer, the local tractor repair said they could not fix it, they could not find the parts. His had a broken front axle - he came by to buy the front axle and spindles.. my father gave him the tractor, plow and cultivator. I still check the model B s for sale looking for it.