Sadly, no, unless I'm forgetting about a special feature in Colosseum you can't buy them. Besides just Item Finding/Trick House, though, you can also find them through Pokemon with the "Pick Up" ability. Mind you it's pretty rare, but it happens.
Ever since the introduction of PP Max I've wanted them to make a secret option that lets you either buy them or win them over and over again. They're one of the best items ever, and I want more! :twisted: