Gee, What do I have to do to get free film?
As for the half frames, some colour film comes as 12 exp rolls which should give about 26 exposures. At ome point there was a "commercial" Kodacolor, which was aimed at folks like real estate people and the like which was a 5 exposure roll. The theory was they could take a cople of shots of the house and get prints back without waiting for the end of the roll.
I think under 24 exp, the cost of the packaging and the work of developing "A" roll would make it more expensive to make smaller rolls.