Wiktionary
vb. (context intransitive idiomatic English) To arrive by chance; to occur by happenstance.
Usage examples of "happen along".
This one introduces us to the Panther Girls, tribes of wild free women who hole up in the unexplored forests and pounce on any unsuspecting males who happen along, and the leader of one tribe, Verna.
But another woman with intriguing vulnerabilities would happen along shortly.
Of course, if someone sufficiently interesting and bold enough to approach her were to happen along, she would not be averse to striking up a conversation, depending on her mood of the moment.
And the chances are if this Frank does not happen along, my friend will marry a young guy in Pueblo by the name of Higginbottom, who is very fond of her indeed, and who is a decent young guy and afterward makes plenty of potatoes in the grocery dodge.
Not only did the most fantastic adventures seem to happen along, but the bronze man's system of attacking the trouble was frequently more fantastic than the trouble itself.
One puff of wind, if one should happen along and scatter that dust among us, might kill us all.
Although I was just thinking of one of the last things Julie said to me, that how extraordinarily odd it was that the dyke-breakers, the palace bombers and the Annecy brothers should all happen along at the same tim.