A big source of lead can be recently sweated copper lines (takes a while for the corrosion control to coat it), but lead solder isn’t supposed to be in potable use anymore. And old fixtures!
Yes I've found it's very frustrating looking for "genuinely zero lead" brass and bronze. Almost all scrap has lead in it to some degree, and even new metal often has a trace.
Neat, this dovetails with another interest of mine, pottery. NaF is "sodium feldspar" and Ca-Si compounds are "wollastonite" among others. Both useful as fluxes in metal casting, in addition to their pottery uses.