Use a variety of search terms. An artist, concept, technique, etc. may be known by various names. If a term/phrase doesn't provide results, try an alternative way of phrasing it.
Use discipline specific sources. Approach your topic from different perspectives. You may need to read anthropology or social science articles to understand your chosen piece.
Accumulate sources gradually and organically. Aim to locate a few promising sources at a time, read and process them, then re-incorporate new information and leads into your topic and subsequent searches.
Place scholarly sources at the core of your bibliography; reviews, reference info, etc. can be used to gain ideas and facts, but are not substantial enough as stand-alone sources.
Archives and Libraries
Video and Audio Materials
General Art World Information and Publications
When analyzing a work of art, it's helpful to develop and apply a list of relevant questions. Consider:
Barnet's A Short Guide to Writing About Art provides many useful examples of analytical questions and is a required/recommended text for most ARTH 100/102 courses.