Problem with this one is it was designed primarilly for drag racing, so the metal needs to be upgraded to DOM (which they can do), but also changes and additions need to be made to the bar design as well.
I believe that AutoPower makes a full cage for the Focus for SCCA Showroom Stock racing.Autopower makes a roll bar. Basically a hoop with crossbrace. They also sell a kit to weld their hoop into a full cage. Other than that, you're best off finding a chassis shop that can make one custom.