I got a replacement rear window for my Triton through Caravancrazy. They were excellent to deal with and sourced a new window direct from Polyplastic in the Netherlands (although it did take a while to arrive). And for nearly half of the cost of an Eriba official window. Can you see a maker's mark on the window at all? That would certainly help you. Mine had a product serial number on a label stuck to the inside of the top hinge.
There's probably far more chance of finding a replacement within Europe, as they have always sold far more over there. perhaps a Dutch dealer would help? Great English language skills in my experience.
Simon