Howdy, Pard,
I can't see how you'd have a holster that would hold hold extra cylinders without being terribly unbalanced and uncomfortable. A pouch that goes on the belt would be more practicable. The safest type would be with a pair of small straps and buckles, but you could make it with a ball stud finial. I would NOT, however, carry it capped! And, yes, I have a pattern for such.