Take some accurate measurements of your fixed window. Then google up "rv windows" or "rv replacement windows"
I did for the heck of it and dozens of sites, suppliers came up. I'm sure you could find one to fit your opening.
Steve & Cheryl + Charlie & Casey, our furry kids.
2012 Forrest River Lexington 283ts
Toad, 2013 Subaru XV Crosstrek
Camping trips this year so far...8