The Diary of George Templeton Strong, Edited by Allan Nevins and Milton Halsey Thomas
One can’t help but notice phrases such as, “If it don’t come to life ...,” and want to scream, “Doesn’t!” However, I believe Mr. Strong is using a subjective construction, “If it do not come to life ...,” which has largely faded from use.
The only current example I can think of is the “were” in, “If I were Queen, I would outlaw teenagers.”