Mandolin chord charts are available on mandolinchords.net, howardknight.net, or bradleylard.com. These sites also explain how to read the provided charts and how to position your fingers appropriately.
Mandolinchords.net also allows searching for individual chords either by name or by category.
Howardknight.net provides an alternative method of searching for mandolin chords. Choosing the desired chord specifications shows the correct position of the musician's fingers to create that note on the mandolin.
Bradleylaird.com offers chord charts sorted by the most common keys performed on the mandolin. Short explanations of basic musical concepts and examples of song tablatures involving the instrument are also available on bradleylaird.com.