Can't help with the repair manual but I've owned a '94 Fleetwood Bounder with Freightliner chassis and with that, I notice that most of the big chassis parts were stamped with Bendix number or it was embossed. Seemed to me that most major components of the chassis were Bendix. Master cylinder is an example that had the number embossed into the metal. So did the brake booster assembly. I would suspect the same of the Oshkosh chassis.
The shocks can be removed and any shop should be able to match them if they aren't too busy. Or you can do the measurements yourself and find a replacement online. I've seen a chart for doing that at Bilstein shocks, I think. Back when I needed shocks for my Bounder, I didn't have numbers either, I found numbers stamped into the shocks. And my 2 fronts were different then the 2 rears so keep that in mind. You might have to remove 2 of yours.
Also, someone that owns your model and year might notice your post...
Good luck. Hey, didn't Freightliner buy all the Oshkosh inventory? You could call them and see if they have a chassis manual?