Prime requisite: indoors. Other prime: clientele must be interested in history of a violent type.
Answer: Gun Shows
I attended several Showmasters shows in the past and enjoyed them. I also attended a relic and antique arms show in Fredericksburg, but Civil War interest often trumps the Revolutionary War.
PA demographics show up well for my book and so I have several shows planned in York and Gettysburg. So we shall see! (Does anyone else ever use the word 'shall' anymore?)