Rough guess, I’d say around the late-1840s. The US Army fielded the 1841 percussion “Mississippi Rifle” as it’s first cap/ball rifle.
By the time of the Civil War in the 1860s, all armies over the world were using percussion locks or variations thereof. Which to me would seem that it had been perfected as a viable system over the course of the years in between 40s and 60s.
I recalled the “personal” percussion caps CS Forester’s Napoleonic Wars Royal Navy (fictional) hero Hornblower’s percussion cap pistols as a private purchased, matched set - but Forester deliberately wrote about them as “new” and “very expensive” . But very reliable.
As for reproduction flintlocks, I'd recommend a former client of mine, Matt Avent, of Tennessee Valley Arms in Natchez, who makes an exquisite Tennessee and Kentucky flintlock. He made a left handed version for me that is a work of art in 54 caliber.