chance upon

“During long periods when it was out of print, Hopcraft's book was the most sought after by customers, a fact which inspires me to buy a copy if I ever chance upon it.”

The Guardian: Confessions of a sporting bibliophile | Rob Bagchi

“By means of this key I crossed it several times with her; but I did not like unexpected meetings, and when Madam de Verdelin was by chance upon our way I left them together without speaking to her, and went on before.”

The Confessions of J J Rousseau