I bought a new hatch for my Captain
from GoMarket.pl - they sell a lot of European trailer parts. Shipping is surprisingly cheap. You can also get parts in the UK (Freedom Trailers) but their shipping is outrageous.
I emailed firstname.lastname@example.org
as he had (some) English. There is a on-line site full of stuff.
Having a friend fluent in Polish helps but not completely necessary.
If you ever need a window, you pretty much have to find a european supplier.