http://www.interpretereducation.org/specialization/aslspanishenglish/ then click the ASL/Spanish/English Resources tab. On that page you will also find Toward Effective Practice: Interpreting in Spanish-Influenced Settings and Hacia Las Prácticas Efectivas: Interpretación en Situaciones Influenciadas por el Español
This resource on English variations in the U.S. is the website companion to the PBS documentary by the same title, in which Robert MacNeil and William Cran traveled the nation documenting and commenting on the accents and dialects they encountered. The book that recounts their journey is also a worthwhile read for L1 and L2 English speakers alike (ISBN# 0156032880).
Interpreting in Multilingual, Multicultural Contexts, edited by Rachel Locker McKee and Jeffery E. Davis: Nineteen international authorities contribute their research and findings to this book. Chapters one through three deal specifically with Spanish/ASL/English interpreting in the U.S. ISBN# 1563684454
Firefly Spanish/English Visual Dictionary by Jean Claude Corbeil and Ariane Archambault: A favorite among many Spanish/English interpreters as well as trilingual interpreters, this dictionary is organized by category (ex. Plants, transportation, architecture, astronomy, etc.) and small enough to take along to assignments. ISBN# 1554077176