You are probably not going to find them, have you considered continental tires? MPT81 are a great tire and come in 20 inch, one of my mogs has them and they run silent and XZLs are very noisey and hard to balance.
Try calling Scott Ingram and Expedition Imports or Jim Ince at Eurotruck, they both deal in Mitche and Conti tires for mogs which are the same size as you need. They will both drop ship to your nearest distribution center.
You don't inherit the world from your parents, you borrow it from your children.
1979 Unimog 416 Expedition Camper
1974 Unimog 421
2004 Dodge Ram 2500, 4x4, Double Cab, Cummins Turbo Diesel
2006 25' Airstream International CCD
2009 Harley Davidson
Sugarloaf, Boulder, CO