On Thursday, May 16, 2019 at 7:54:13 AM UTC-5, Home Guy wrote:
I'm installing a couple ceiling fans in adjacent roons and was going to
install the switch controls on opposite sides of the same wall, at the
same location.

I'm thinking there is, of course, such a thing as a two-sided,
through-wall outlet box. Because 2x4's and drywall are standardized
enough so you can make a box that will work for this application -right?

I do some web-searching and come across some post in some DYI forum from
10+ years ago where someone is asking the same question, and no, for
some reason there is no such box.

I also come across this:

https://www.youtube.com/watch?v=pg7XdoBnKjU

Seems to be a video made by someone who patented a through-wall
double-sided box. Really? A patent for the obvious?

It's crazy that these don't exist.

To hard to see from here what you have or what your codes are but in the Chicago area were everything is in steel I would use two 1900 boxes back to back with drywall plates and a back to back connector ( Rigid Box Spacer )