Yes, Berdick (Canadian company) made the larger jalousies for some of the mid-70's Bolers. One note that might help you in your search is that the non-Berdick windows
I have seen (in a later 70's Boler) are very very similar, and I don't think you would have a problem replacing your window with one of those. In other words, any of the similar, square-cornered jalousie windows
from a Boler
, etc. 13-er would probably work.
As far as I know, no-one makes the square-cornered ones new anymore. And yes, you can fill in the corners with fiberglass and use radius-cornered ones, but that would not be desirable to me because I would then want to replace all of my windows
so that they were all matching and all black (ours are silver). That would turn it into a much-larger and more expensive job. Also, the new jalousie windows
of the size that fit in our dinette area only have 50% of the opening area of our square-cornered ones.
Luckily for us, some people prefer sliders and so change their windows, and you may find one
If not, here are some places where you can find repair parts:
Vintage Trailer Supply:
Vintage Trailer Supply - Vintage travel trailer parts and supplies!
RV Parts and Motorhome Parts Online Outlet
Interstate Metal Fabricators, Inc.
I have done some parts replacing on mine, so I may be able to help with specific questions (although it was mostly seals).