This is the first citation of the phrase in the OED:
[1965 H. Rhodes Chosen Few 179 ‘He..finally told me what page he was on’. ‘Is it th' same page you thought it was?’]
The next citation, which uses the phrase in its current form, is from 1979:
1979 N.Y. Times 18 Jan. b7/2 One of the things that happens when you makes as many rule changes as the National Football League has had a propensity to do in the last couple of years is that it takes a long time for everybody to get on the same page as far as the rules are concerned.
It was doubtless used in speech even before, and the paucity of written references is, I think, due both to the fact that it originated so recently and to the fact that it might have been considered slang at the time. (The OED categorizes it as colloquial, being used chiefly in the United States, and slang.) The first sentence, I think, makes somewhat clear the motivation for using such an expression.