You want to to see if Print Wizard will work for you, but first you have to figure out the plumbing; that is, how to get print data from your existing application (or one you're about to write) into Print Wizard. There's so many options!!! Let's see if we can narrow it down.
If your app runs on Unix, Linux, AIX, etc.
See the attached PDF for info on this subject.
The Millennium library automation system, available from Innovative Interfaces, Inc. (III), can print spine labels or spine/pocket label pairs. However, this printing support is fairly basic. Print Wizard Service Edition (PWSE) is a product from Rasmussen Software, Inc. that can enhance and adapt the output from Millennium on its way to the printer.