Has an International Rugby game ever ended 43-18?
Exactly once. On June 17, 2006, Australia beat England 43-18, and no International Rugby game before or since has ended that way. When it happened it was a scorigami, the first 43-18 in league history.
That makes 43-18 the 510th most common final score out of 844 that have ever occurred in International Rugby. One point away, 44-18 has happened never and 43-19 has happened 1 times.