holster certification is usually intertwined with Holster Qualified. What that means is, that some clubs don't want you to just show up site unseen without ever having used a holster before. Not a good idea anyway. IDPA (and most other disciplines) want you to have some experience with the equipment you are using, and that is garnered through private practice. The Black Badge is mandatory for IPSC, but only a small part of it is holster training, most of it is shooting training. If somewhere you are going absolutely has to see "a piece of paper" I suggest the IDPA orientation course. This course again is only a little about holster usage and mostly about gun manipulation and the rules of IDPA. The course is pretty much free, but you generally need to be a member of IDPA to be allowed to take it. The CDPA course is basically exactly the same, just the CSSA is the one who administers and charges for it.
You could be just as well served to practice with someone who is a very experienced shooter with a holster, and have him show you the important things, then just repeat, practice and learn.