It's even worse, this reference is not to "Maine Farmers' Almanac" but to "Maine 'Farmer's Almanac'", i.e. the formerly non-Maine FA now published in Maine, but unrelated(?) to the former Maine Farmers' Alamnac. 
 The last confirmed "Maine Farmers' Almanac" is the 1968 issue, "No. 150". 
 Something must have happened after 1968. For the period 1969 to 1973, "Maine Farmers' Almanac" still appears in the Catalog of Copyright Entries but I am not sure if it actually still appeared.  
 Geiger's FA moved to Maine in 1955, and it is plausible, I suppose, that the "native" Maine FA was killed off by the competition.