Oh that's sad about your egg being hit; but yeah, thank goodness it was not worse.
I have those same windows
on my Boler
. They were made by Hehr but are no longer in production. You're right that they were installed in many campers back in the day - even in stickies and truck campers, etc. So your best bet for a complete replacement would be finding one for sale
used or in an RV salvage yard.
That said, many of the parts are still available - how bad is the damage? Vintage Trailer Supply, for example, has the gaskets and seals, the operator arm, and some of the arm parts. Interstate Metal Fabricators and Pelland Enterprises may also have parts.
If you do have to go new, then there are new ones available, but they have radiused corners, so you would need to do a bit of fiberglass work to fill in the square corners. Scamp's parts department has them (their window prices are far better than I have found elsewhere). They are the same general size but just with the radiused corners and a black finish.