Sometimes the best resources for undergraduate assignments on LGBT topics are not specialized ones, but rather contained within mainstream publications and collections.
Common research resources like the Census or collections within large university archives have a lot of information about LGBT issues. These are often available to everyone on the web or at public libraries, meaning there are plenty of ways to do LGBT research beyond big university libraries. For instance...
There are many research guides published by librarians and other experts on LGTB issues, general topics and specialized topics like the law. Here are just a few examples.
Just a sampling of where to search for LGBT government documents. For a broader swath, search Google: [gay lesbian inurl:gov], for example.
Beyond well-known LGBT archives, a number of universities and libraries have major LGBT collections. For example:
LGBT newspapers are included in this database, available from many libraries.