For more sources (e.g., for a particular Circuit), do a search in the MLaw Catalog using "jury instructions federal." Many courts also publish pattern jury instructions on their websites.
To find jury instructions for a specific state, do a subject search in the MLaw Catalog using the term "instructions to juries." Many states also publish pattern jury instructions on their websites. Some states may include pattern jury instructions with their court rules.
Lexis and Westlaw each have extensive jury instructions databases.
