Well, if it isn't downloadable for 12.1.2 in the CA Marketplace, chances are it's not yet available for that release.
I guess it depends who provides the action pack in question. If it's something "official" from Automic, posting an "Idea" or quizzing your sales contacts about a release schedule it might be the way to go. If it's a community-provided action pack, it's a volountary effort by some kind soul. The author should be listed in the "Credits" section, in which case there's probably no harm in shooting him an email and asking nicely for a 12.1.2 release. Usually with software written by volounteers in their free time, sending them a crate of beer or other sort of bribe may or may not help, too
Hth,