The Collaborative International Dictionary of English v.0.48:

Producent \Pro*du"cent\, n. [L. producens, p. pr.]
   One who produces, or offers to notice. [Obs.] --Ayliffe.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

PRODUCENT. He who produces a witness to be examined. The term is used in the
ecclesiastical courts.