I imagine b/w MP film overall is slow in sales...but specifically negative MP stock.
Mostly used for 'effects" shooting these days.. which is done by the high budget productions so they are less likely to sell their ends.
The colour neg ends are fairly plentiful, but the REMJET is a pain. The B&W stuff does not have the remjet. folks like "certified film" are likly to have the 35mm ends for the colour stuff.
The 35mm movie film does have slightly different perforations, BH1866 vs KS1870 but that should not be noticed by a still camera. The film is only numbered every 18 inches so you are on your own if you need frame numbers.
MY guess for the Arista Premium is Plus-x reversal, as it is rated at 100ISO, and the movie data sheet indicates it can be processed as a negative. Kodak only sells it in 16mm and super 8, but they consider it a valuable product as the major buyers are film schools who assign it for student projects. From Kodak's point of view they want the students to get exposed to using film so they will know the difference compared to video type production.