The best thing that I could suggest to you, would be for you to call a few "truck" or "RV" salvage or wrecking yards... maybe they could send you in the right direction.
What you'll want to ask for, is a replacement dash for a Chevrolet P-32 cab or chassis. You never know what you might find out there!
It's possible that even GM/Chevrolet/GMC would happen to have an old stock replacement part... It MIGHT be 'spensive that way, though! Just for fun, call the "big" Chevy dealer's parts department in your town.
Another option would be to look around on craigslist for a person "parting out" a junk motorhome... It doesn't exactly have to be an Airstream/Argosy... it's just gotta be a motorhome that was built on a Chevy P32 chassis.
Try searchtempest.com to look around on ALL of the craigslist listings... You can type in a "mile radius" for how far you're willing to travel to get what you want.
And don't forget that ANY 1973, '75, '78 etc, etc, P32 dashboard will work.
The P32 cab was ALWAYS the same width, and Chevy, NOT Airstream designed and installed that dash on the chassis BEFORE the chassis was sent to A/S for the motorhome body.
The GM P32 was a very popular chassis back in the 1970's-1980's to use for a motorhome, and many makes were built that used it...in other words, you might find the dash out of an old Revcon or Barth or something. It'll work for you.
Even if you found one that was pink and needed it to be chartreuse (or whatever) ... You can clean it up and use spray enamel paint on the hard plastic, and Duplicolor also makes a GREAT vinyl dye to use on the soft parts.
Have fun in the search, and be sure to holler if you need me to throw in my 2 cents worth...OK?
Slick (and Kathy)