> you had to make them yourself

Well... not quite...

> Up to fourteen young male slaves, aged ten to twenty-one, worked at the forges of the nailery. From 1794 to 1796, while he was in temporary retirement at Monticello, Jefferson calculated the efficiency of the nailers, each day weighing their nail rod and the nails they produced.

(Source: https://www.monticello.org/site/research-and-collections/nai...)

Though it would seem the idea was to then sell the nails for extra income (TJ was always strapped for cash), so it's kind of an ugly stop on the way to "what if you could just go buy a bag of nails?"