the part# is H4X28 for the 1in.,,, description of o-ring is 4x28 buna 70 metric o-ring. I believe Motion Industries got them from APG Ohio 1-800-883-7457.. being these were a special order I had to order 50 of them, still less then the cost of 1 fitting. I did get them relatively cheap. I only used 6 of them so if someone needs a few of the 1in o-ring for the shark-bite fitting I will pass the savings on to you. e-mail gets my attention.
by the way the one I had leaking was my fault, I pinched it during install 3 years ago, late last burning season it decided to start dripping when I shut the flow of hot water off during warm days , then seal itself when I would turn the pump on in the late evening.
the 3/4in. o-ring is close enough you can find it in any good parts store, but not the 1in. jim