"The facts" are that beginning with Elisha Williams in 1744, American preachers cited "the celebrated Lock," and Locke as "the noble Assertor of the Liberties of humane Nature." Peter Whitney cited "the great Mr. Locke" for his ideas; Samuel West (in his sermon that is second to that of Mayhew in terms of influence) identified "Mr. Locke" as the source of his ideas. Samuel Cooper said that the "principles and arguments" he was using were "grounded" in "the immortal writings" of Locke. John Tucker had an extensive quote from "Lock on civil Government" in the crucial part of his best-known sermon.
[C]an [anyone] identify a single Patriot sermon that cites Calvin or Beza or "justifications of political resistance found within Reformed Protestantism." [A]s always, I'm open to such evidence. In Donald Lutz's acclaimed study of the influences on American Revolutionary thought, there is not a single Reformer in the list, but Locke is 3rd in terms of citations. Dreisbach's chapter on the Revolutionary sermons spends 18 pages on the 16th & 17th century Reformed guys and then 6 pages on actual American preachers -- almost exclusively Mayhew. He includes no citations by Patriot preachers of any of the Reformers he had introduced as the fundamental influences. Dreisbach is, of course, right that Mayhew does not cite Locke AND that he doesn't cite the Reformed guys either.
So, whose arguments/principles are reflected in Mayhew's sermon?
Mayhew's entire argument fits and flows perfectly from Lockean presuppositions and principles, but it includes elements completely foreign to the Reformers. Most notable of these is emphasis on a state of nature -- an idea anathema to Reformers who believed in the biblical record of the beginning of man and society as recorded in Genesis.
Mayhew -- and the other Patriot preachers -- did not speak of "covenants" as did Knox et al, but rather of "contracts." They did not speak of "lesser magistrates" or of "interposition" or any of Beza's creative notions. Their arguments went right down the line of Lockean thought -- which is why Tucker seamlessly included extensive quotes from Locke in the middle of his sermon. Additionally, for his part, Calvin explicitly rejected any notion of rebellion -- as did Luther. So two of the most important and prominent voices of the Reformation were not even available to those who might have wanted to make Reformed arguments.
Again, as I note in my first book ..., this is a primary reason that Mayhew's sermon was so influential. Those raised in Reformed churches and taught by Calvin to be subject to authority -- even tyrannical authority -- found in Mayhew a plausible excuse to rebel against an authority they found inconvenient or disagreeable. Mayhew's sermon was groundbreaking because it was new to those people -- not because it rehashed what they had already been taught.
....I think it's true that reformed resistance under law may well have softened up the congregants in America, making them more amenable to the arguments of Locke. But when we examine the sermons, it's Locke and not Rutherford et al. And, in a nuanced sense, Locke teaches something different from Beza et al. The difference between resistance under law and revolution.
Parts of the Declaration of Independence speak in the language of resistance under law; these are the parts where the Patriots made the claim that what Great Britain was doing violated British law. Other parts of the Declaration are revolutionary; those are the Lockean parts.
This is somewhat complicated. Locke was cited in sermons. These sermons understandably also cited the Bible. In Lutz's above mentioned study, Locke was cited during the period of time when the Bible was constantly being cited (the revolutionary period, the DOI). The later period when the Constitution was being framed and ratified, Lutz notes the biblical references dry up and it was more Enlightenment and other sources.
Yet I've also seen it argued (I think from Robert Kraynak) that references to Locke also start to dry up during the period of the Constitution's framing and ratifying. That those Enlightenment sources are non-Lockean. More Montesquieu than Locke.