The Biblioteca Italiana of the Università degli Studi di Roma "La Sapienza" features the full text of the Discourses in Italian on their website!
The site also features a search function that I found quite useful.
The site suffers from only one problem that could cause confusion. Book Three has been incorrectly grouped with Book Two, so that the initial page you see as a visitor only appears to contain a collapsible table of contents for Books One and Two. If you want to access chapters in Book Three, simply expand the table of contents for Book Two and scroll down; Chapter One of Book Three will immediately follow Chapter Thirty-Three of Book Two.