I found an article about possibly doing this in the .NET version, but I am working in Access, and the events seem different enough where I am not sure. I am studying it, but thought I would ask, maybe someone has already figured it out, or others might be interested in the answer. 

Private Sub IGrid2_VScrollBarScroll(sender As Object, e As iGScrollEventArgs) Handles IGrid2.VScrollBarValueChanged
IGrid1.VScrollBar.Value = IGrid2.VScrollBar.Value
End Sub

Private Sub IGrid1_VScrollBarScroll(sender As Object, e As iGScrollEventArgs) Handles IGrid1.VScrollBarValueChanged
IGrid2.VScrollBar.Value = IGrid1.VScrollBar.Value
End Sub

I am going to look in the Access code samples too, but if anyone has a hint, I'm all ears!

Slightly different in the ActiveX version, but this works in Access2016.

NOTE: I only have vertical scroll bars, so I don't check eBar for the correct bar, but I could

Private Sub iGrid1_ScrollBarPosChanged(ByVal eBar As Long, ByVal lValue As Long)

iGrid2.VScrollBar.Value = iGrid1.VScrollBar.Value
Exit Sub
End Sub