Does anyone know how one would say "sources of law" in Latin?  I have loci lex legis, but I'm not sure that's correct.  

Did a bit of research and Loci lex legis sounds like it would be translated as: causes/positions (law) of law.

Maybe Orti Legis-"beginnings of law," or, "origins of law."

Lex is definitely the word for law, but the word "locus" doesn't seem to fit all that well.

This page has a list of words that might for the word, "sources":

http://catholic.archives.nd.edu/cgi-bin/lookdown.pl?source

another word might be "origin." in which case, I think "origines legis" would be what you are looking for, literally, "origins of law."
I'm not one hundred percent sure of that's the proper way to write the nominative plural of Origo, but i think it's right.