I know from John that the stock he sells is Kodak perforated, Colorado works. Since transfer from there it's been Rochester made. Kahl and Wittner, both Germany, have perforators.
Don't forget that Cine-X alias Plus-X reversal has a grey acetate base, log density 0.23. You never have clear whites on your screen, 40 percent of the light is lost at the film base. Same goes for Tri-X reversal, actually all Kodak Ciné reversal stocks since Panatomic-X but that is some time back.