Have you tried SBS? That is where we buy most of our textbooks.
By the way, you might want to look into the SIELE exam. It is new and offers advantages that the DELE doesn't. For example, you can take the exam in parts (oral production, written production, reading, listening), the results come in sooner, and there is no pass/fail, just a final grade, much like the TOEFL. Btw, El Sol (my school) is an authorized SIELE testing center in Lima (www.elsolperu.com
The Cervantes Institute (who are behind the DELE) are also the main backers of this exam, together with the University of Salamanca, the Autonoma de Mexico, and the University of Buenos Aires). The technical partner (since it is a computer based exam) is Telefonica.