Sorry about your water leak and losing a window.
Here are some RV parts sources:
RV Parts and Supplies | Rv Accessories | RVPartsCountry.com
https://www.rvsupplyparts.com/
RV Supplies, RV Accessories & RV Parts for Motorhomes, Travel Trailers - Camping World
ShopRVparts - RV Parts and Supplies
RV Discount Suppliers Home page
RV Parts, RV Accessories RV Supplies Priced Low
Discount RV Parts-RV Parts and RV Accessories-RV Parts Online
RV Parts Nation
RV Parts & Accessories Texas, USA - Tweetys.com
RV Supply Warehouse | RV Accessories and Supplies
Home page
https://www.rvupgradestore.com/
https://dyersonline.com/
Best of luck on finding the correct sized window.