Testing for trace minerals is quite tricky and the procedures can be elaborate if done by chemical means. Note that the lead will generally be in the form of a soluable compound like lead acetate, or lead carbonate or whatever. In many cases other chemicals, especially chlorine, if they are present can interfere with obtaining accurate results. If you go to NIST's web site, you can probably find the standard procedures (which is what the labs do). Doing these procedures probably requires a well-equipped lab, and also probably takes a considerable amount of skill and practice. You can't just read a few instructions and get it right off the bat if you are not an expert chemist.
There are two alternatives:
XRF machines. They cost $30,000 and up. Check with a manufacturer to find out their senstivity.
Spectrographic analysis. If you can obtain access to a high-quality spectrometer, you can easily do a test. It may require some filtering. Just tell the physicist who runs the spectrometer that you want to test for trace amounts of the compounds you are interested in (lead carbonate, etc). This kind of instrument can identify very tiny amounts of any element or compound reliably.