This is the link I am using: https://www.britishairways.com/trave.../en_gb?cabin=F

This is the list I compiled from it

AUH ABV ATL AUS BAH BJS BDA BOS BGI CPT ORD CVG DFW DEN DOH DXB GCM HKG IAH JNB KWI LOS LAS LAX MEX MIA NBO BNA NAS MSY NYC MCO PHL PHX RUH SAN SFO SCL SEA PVG SIN SYD TPA HND YYZ YVR WAS

The problem I have is that not all craft going to these routes have a first class cabin so this list is theoretical only - I use ita matrix first to confirm if the cabin exists and then EF to see if agrees

To illustrate my problem - if you try and book a BAH holiday through Doha and use First Class, I get no results - If I use flight finder for the same dates, it finds the flight with first class.
I was wondering if it was even possible to find a first leg in first class for any route but I was able to for flights to INC so it is possible.

I'll have to ring up and book, seems like there is no surefire way online.