I highly recommend searching archive.org for books and other items related to the War of Independence. The materials available there are digitized and, if the public domain, may be downloaded (often in a number of formats including PDF and Kindle). Many not in the public domain can be borrowed with a free membership.
One of the groups of materials I came across this evening are manuscripts and documents held by the Boston Public Library. Included in the material is the certification of Isaac Davis' death by Abijah Pierce, an account of the damage done to the estate of John Hancock by the British during the siege of Boston, a deposition describing the Boston Massacre, and one handwritten manuscript entitled "American casualties in battles of Lexington and Concord, with other deaths to May 1, 1776." The layout of the last item resembles the "Bloody Butchery" broadside.
https://archive.org/details/bplscarwm (https://archive.org/details/bplscarwm)
In Liberty,
Greg Seneff, Sr.
"Bluegrass Colonel"