I linked a chapter in the book. The whole book is there. Please quote chapter and verse. As I say, I read it recently, twice, and don't think that he has anything good to say about mercenaries. I could have missed something, but certainly his main opinion is in the chapter that I directed you to, [link|http://www.constitution.org/mac/prince12.htm|CHAPTER XII: How Many Kinds Of Soldiery There Are, And Concerning Mercenaries].
Lots of people think that virtually anything cynical about power politics is backed up in Machiavelli. Until I read his work, I thought the same. But when I read his book, I found it remarkably consistent. Unpleasant, but consistent. And one consistency is that he disliked mercenaries.
Cheers,
Ben