Must have been a special order for that model Graflex as Cooke only list 5 1/4" and 6 3/8" f2.5 lenses during that perion. That's not unusual though as TT&H made lenses specifically for some Thornton Pickard reflex caneras and Kodak had been using Cooke lenses on some cameras for over 20 years.

I'd forgotten that Eastman Kodak were the distributor for TT&H Cooke lenses in the US in the 1930's, Kodak Ltd were the distributors of Ross lenses in Australia & New Zealand.

Ian