tht would be the 6.5x9 size which is I believe is also referred to "2.5x3.5" and seems to be uncommon in the US.
I did a quick search and it looks like the Medalist setup is for 6x9 or 2.25x3.25
For for that size there is generally Foma/Arist 100, 400 and Ilford FP4+ and HP5+.
Best place to get it in the US is Freestyle, but they're not listing the Arista 400 at the moment:
Freestyle has the largest selection of 35mm black and white film from every major manufacturer like Kodak, Fuji, Ilford, Arista, Foma, Woflen and Cinestill. In addition, we carry a complete line of 120 film and sheet film in stock and ready to ship.
I don't know if the Medalist uses normal sized film holders or custom, but te page did say that it changes the location of the film place renderng the rangefinder useless, and requireing focus using ground glass.