While I was searching for parts and seals for the windows
in my 1974 Boler
I came across the manufacturer and importer that distributes almost every part and seal made. Strybuc Industries
. They will not sell to you directly but they have retailers throughout North America who handle their products.
Here is the Strybuc RV Window catalog
Check their website for sales contacts in your area (contact are at the bottom listed by State, the sales rep. will reply with the retailer closest to you. Strybuc Industries - Contacts