The postmaster at Ed Kentucky was one of the most cooperative/prolific sources of fancy cancels during the late 1920s and early 1930s, many on registered covers. A quick search of
ebay reveals about a dozen covers offered at the moment.
Loso & deWindt's "20th Century U.S. Fancy Cancelations", revised edition by Fishback & Dell in 1987 lists about 45 different ones from Ed, not to mention ink color variants on some. It would make a challenging collection.