To find librettos:
WorldCat is a world catalog of libraries that participate in SU Libraries' inter-library loan network. Search here for books, scores and recordings in other libraries, and we will borrow it for you, free of charge.
Find something you like? Collect the citation and place an inter-library loan request. PDFs of articles usually arrive in 1-2 days, and books usually arrive in 5-8 business days.