Oh, https://nsr-leisure.co.uk/ are now stocking Karosser demountables (now branded as Northern Lights Campers)

I did find this... https://www.leisureshopdirect.com/ventilation/camper-van-conversion/seitz-windows/dometic-seitz-s4-hinged-windows ...and this... https://www.leisureshopdirect.com/ventilation/camper-van-conversion/seitz-windows/dometic-seitz-s5-hinged-windows ...which might include a more recent m...

Strange you should ask.
I'm trying to find a complete AGP60500x0300 unit also for a Nordstar.
Dometic and Seitz don't appear to consider that the window ever existed.

I'm thinking that I'll need to contact Jens Heidrich at https://wohnkabinencenter.de/ since they are probably the experts.