https://www.scientificamerican.com/article/ancient-roman-lea...
I saw a talk on one of these experiments while I was a grad student. Apparently their lead source had "historical significance" according to the government of France, and getting it out of the country required beurocratic maneuvers of questionanable legality.
But what compound? PbH4 isn't stable. PbF4 is barely stable. Maybe Pb(CH4)4 ??? Naively, I guess that you'd get even better mass resolution. Molectual mass of UF6 being ~352, vs ~267 for Pb(CH4)4. Good use for all those leftover centrifuges ;)
Well, it would be infinite until you run out.
Edit: it appears that someone disagrees with me. No worries, healthy disagreement is a good thing.
But I'm curious: how would you produce an infinite amount of product?
I won't worry about it further, time to go enjoy my unlimited internet.