The one sold by April 30's store fits. I believe the only one that fits the FW feed dogs correctly is made by Alpha Sew. All others are too large. Similar story for the 301, but there are no walking feet to correctly fit the feed dog width of the 301's.
http://www.april1930s.com/html/walki...herweight.html
Others may carry the same brand, but this is the one you want.