Just because you don't find something listed in the Libraries' catalog doesn't mean you can't get it, and get it fairly quickly. Try these.
Search@UW -- Because it searches all of the UW system in its default mode, it facilitates borrowing materials from other UW schools very easily.
Illiad -- InterLibrary Loan interface which allows for tracking of your requests and provides access to scanned articles when they arrive. Books/scores can still be requested directly through WorldCat, but this works well too
-- Provides links from a citation to the full-text of the article if available or to other ways to get the article. A very useful tool is that it will 'populate' an ILLIAD form if needed. See the "Get It" help page for more details
WorldCat -- Confirm the existence of a book, score, or recording and place ILL requests for them - note that there is now http://www.worldcat.org which you can search from anywhere, but you can not make an ILL request through it. You must log in to WorldCat through the UWM Libraries in order to do so.