I once held an original DB shotgun, 12 ga. made in the Tower Armory, in London England, in 1776 or 7, that came from a private collection in St.Louis, Illinois. The barrels were 36 inches long. LOP on the stock was only 12 1/2 inches. It balanced like a dream.
My point here is that the lock had the military double throated locks on both sides, and they were the large, Brown Bess locks, you see on RH military rifles. So, the answer to your question must be " YES", LH locks were made, but they probably cost a fortune, and only the very wealthy could afford them. Someone said a LH French Fusil lock was dug up somewhere in a dig in Louisianna a few years ago, so LH locks were also known to the French. Anywhere you see a Double Barreled Flint shotgun, whether made in Germany, Austria, France , Holland, Denmark, or England, you are looking at LH locks. The fact they exist means they were available for the right price to be used on single barrel guns, too. Sport shooting did not really come into vogue until the last half of the 18th century in Europe, or the colonies. Even then, only the aristocracy had either the time, or money to indulge in the sport, and own the firearms needed to do so. Much earlier than that( and you will find earlier firearms) you are looking at guns that were made for royalty, usually with the hope that the royal would make the gunbuilder his personal armorer, and put him under stipend,( a regular pay check) and pay for his place of work, his apprentices, etc. so that he could afford to do the kind of delicate, and time consuming work that would make him rich and famous.