Search out, find, obtain, as in I'm sure I can dig up a few more supporters. [Mid-1800s]
dig up some dirt or the dirt. Find derogatory information about someone or something. For example, The editor assigned him to dig up all the dirt on the candidates. The slangy use of the noun dirt for “embarrassing or scandalous information” dates from about 1840, but this metaphoric expression is a century newer.