From what I'm guessing, most of these PMs as of late seem to have to do with these products being up in certain places but not for sale by the person posting about it. So unless I'm wrong, that wouldn't really go in CB.
But, I think the best way to do this is just look out for fellow members. If you see them saying something like "I wish I could have gotten my hands on '____'" and you know where they can get it, just send them a PM. It does get to be too much when you see so many posts saying "PM me if you want/have this".