Giulio Pons has a quick post with a code snippet showing how to grab the possible values for an ENUM or SET field on a MySQL database.

This function returns an array with the elements allowed in a ENUM or SET mysql field. This can be usefull if you’re making some automation and need to retrieve those values without writing them in your code.

The function uses the database's metadata to get the column information for a table and filter out the "enum" information from that. The column information includes the set of values possible and a few simple string handling functions make it easy to grab them. They could also be replaced by a regular expression or two to grab the same information more concisely.