The pilot reported that after landing on runway 12, the airplane began to veer to the right. The pilot's attempts to maintain directional control were unsuccessful and the airplane departed the right side of the runway. After departing the runway, the airplane struck a plastic storage container and another airplane that was tied down. The impact damaged the right wing strut. The winds reported at the airport about the time of the accident were from 080 degrees at 5 knots. During a subsequent exam of wreckage, a Federal Aviation Administration inspector found that the forward clevis fitting and attaching hardware were missing from the left hand tailwheel centering spring, which caused the airplane to be uncontrollable. The clevis fitting and attaching hardware were not recovered.