Busier than...

Just an observation and guess:
I have seen the phrase used in the New England area. There is usually a few more words tacked onto the end of the phrase--"busier than a cranberry merchant in November"--the reference to cranberry being used for a traditional Thanksgiving feast.
There are tons of "busier than" expressions:

busier than a one-armed paperhanger

busier than a hooker on a troop train

busier than a one-legged man in an ass-kicking contest

etc etc

As a bartender on payday
As a w h o r e at a picnic
As a bare-foot boy on a red ant hill
As a cat with its fur on fire
As a pup with two (fill-in-the-blank)
As a goat with three (fill-in-the-blank)