Have you asked from Kuttilan lasi, same place where you get your windshield. Maybe they have it already or they can do it from your mockup model, they will give an advise how to do it.
This is one option if you don't find original one.
Regards
Mika
ImpJay is right about Kuttilan Autolasi here in Finland, it's well known shop for every kind of car class, also custom made. Call them or give them a email.
Regards,
Mika