april1930s.com or sew-classic.com for the 301 or sew-classic for both machines. Download a free instruction book from sew-classic or ISMACS to see the directions for putting the case back in. You have to remove the needle plate and get the little finger in the slot on the underside of the plate before you tighten the screws.
April specializes in featherweights and 301s. Jenny at sew-classic has a lot of vintage machine parts, both new and reproductions.