american sign language
DEAF -- Means of communication
I would suggest starting with Multiple EBSCOhost Databases.
Then, check out Proquest Dissertations & Theses.
Other databases you may want to check will depend on what area of ASL you're researching. If you're researching the educational aspects, then you may want to try some of the databases on the Education Guide (ERIC was already included in the above Multiple EBSCOhost Databases search). If your research is more science-based, then you may want to search ScienceDirect or Wiley Online Library.