Try Brown Leghorn Society:
http://the-coop.org/leghorn/
NPIP:
http://www.poultryimprovement.org/statesContent.cfm
NPIP uses stock codes for the breeds. Here are the Leghorn codes. It appears that Mille Fleur Leghorns are only listed as Bantams, but I'm attaching the codes for both Regular size ("R") and Bantam sized ("W") codes:
View attachment 2105267View attachment 2105268
Regular size:
View attachment 2105269
When you go into a state, a document opens up. Use the Find function on your computer to search the document for that code. For code W118, nothing came up in the TX or OH (where I live) documents, but you can search the other states. Of course, when searching for some of the more common Leghorn varieties, there were some results. Good Luck.