Oldbusguy,
Speaking of Viking fenders being hard to find, I did a little web searching and found a couple of buses (both 1959s) that use the same front fenders as the 1958 ones (I think) being offered for sale on FB Marketplace.
Neither "bus for sale" was remotely close to your noted Michigan locale (1 in Kentucky and 1 in Texas), but in looking at the pictures in those ads, it adds a further question on you fender needs.
I snagged and added a couple of the bus pics below from those ads and they show a fender that is quite different (at least on the trailing end) from the Standard Viking truck fenders.
It would help fellow Bolters offer more help or leads on a replacement fender if you could post a picture or 2 of your bus. Need to know if your fenders are the same as those in the pics below or the same as standard 1958-59 Viking truck fenders???
PS - While you ponder a reply and possibly post some pictures of your bus, here is a
1958 Chevrolet Truck Engineering resource document you may want to read through. Lots of info about the Viking truck line (Medium Duty Trucks) that directly applies to your bus.
