Oh Wow, no steps ever? I wonder if maybe some PO removed them and closed in that area under the door for some reason. You can buy the original steps from the '70's again as Airstream reintroduced them on new trailers a few years back. If your camper truly didn't come with steps from the factory, you may have to add a couple of outriggers under the door that have cut-outs specifically made for that old step design.
I'm pretty sure Out Of Doors Mart sells those outriggers and steps, but I could be wrong. Airstream, Salem, & Rockwood RV's for Sale - Out of Doors Mart
Take a look on-line for "standard/generic" steps that other manufacturers use as well. I'm guessing they'll be cheaper to buy, but will probably require some type of modification of the frame area under the door.
I'll send you phone number via PM and we can talk sometime.
Good Luck and have fun with it.