actually I found this site (and your topic) on a search for this vehicle in any scale. I see only 1/18 models diecast and plastic kits of the 4 wheel carriage.
I think you'd have to fabricate the parts yourself, and if you made a small run of each part needed, you could be THE Source of them.
actually it is the same with a full-size reproduction. only some 1-offs exist but plenty of demand!
my plan and advice would be to study as many photos as you can find, and read Benz' patent application #37435 for specs.
Good luck!