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At the Dane County Farmers' Market in Madison, Wisconsin, Weston's Antique Apples sells them for maybe one Saturday in late August. I was lucky to be back this week to attend meetings and am trying to find out if any farmers sell these in the Baltimore/DC area.
For more information:
"The Pears of New York" by U. P. Hedrick published in 1921: https://archive.org/stream/pearsofnewyork00hedrrich#page/n7/mode/2up [Seckel appears starting on page 215.]