Evanston, Ill.-Twenty wins in four years is quite an accomplishment for even the best Midlands wrestler. In the 38 year history of the Midlands Championships only 11 can say they are apart of the "20 in 4" club, but this year as many as six new members may become part of the elite group.    Iowa State senior Cael Sanderson could become only the second wrestler in the tournaments history to reach the "20 in 4" mark without a loss. He is 16-0 in his three trips to Evanston. The last one to do it undefeated was former Cyclone Dan Gable.    The 133-pound class could see two new members emerge. Roman Fleszar, a Hofstra graduate, finished third last year and needs only four more wins to put him in the "20 in 4" club. Former Michigan State Spartan, and a 1988 Midlands champion, Pat McNamara will be back looking for five victories for his invitation.    149-pounder Eric Schmiesing, also a Hofstra graduate, is 15-6 in his three Midlands appearances. He placed third at last year's tournament.    In the heavyweight division, Ohio International Wrestling Club member Mitch Clark needs only three wins in his fourth appearances to enter "20 in 4" status.    If all six men reach 20 wins this year it will be the largest group of inductees in the 39 years of Midlands wrestling.