Responding to the alleged mistreatment of fellow country artist Ricky Van Shelton by a television producer, Waylon Jennings has called for formation of an artists association.Jennings’ comments come in the wake of Van Shelton’s expulsion last week from a TV taping for the 35th anniversary celebration of the Country Music Assn. (Daily Variety, Jan. 18). Van Shelton got the heave-ho from producer Irving Waugh when Van Shelton refused to sing part of an Elvis Presley song. Waugh has since apologized. The Tennessean reported yesterday that Jennings was upset at Shelton’s alleged mistreatment. Jennings could not be reached for further comment.