Unless you need for the lid to fit securely, you could just fashion a new cover for the jar. Years ago, we used to make doll hats, by soaking a circle of felt, in white glue and water (mostly glue). We'd mold the wet felt over a cap (close to the doll's head size), secure it with rubber bands, then wait for it to dry. Once dry, the rubber bands were removed and the hat held its shape. You could do something similar, over the top of the jar.