To kinda close out the question whether or not a 295/75R22.5 would fit, I'm guessing "maybe". In case anyone runs into a similar situation and cannot get a tire.

It appears that size is available from Goodyear and Toyo. Michelin does not seem to carry that size.

As best as I could compare against dis-similar tire charts, it seems that the tire radius are:

315/80 - 42.3 in
295/80 - 41.3 in
295/75 - 40.2 in

So, it's a good two inches smaller than the 315/80. Someone other than I will need to comment whether or not that could co-exist (on the tag) with 315/80's on the drive axle.

Ray