I've not seen gullwing windows in the flesh yet, however I'm looking at a set as part of my build.
current front runners (har har) are MobileStorageSystems
https://www.mobilestoragesystems.net/products/side-door-and-frame-mss-sdaf?_pos=6&_sid=ee166146c&_ss=r&variant=17638049671
and the fancy...