Hm, that's a good point Kelenas about the Shugenja heavy minor clans... OOOH! IDEA! The Centipede Clan is presently still extant! They're a matriarchal clan of shugenja who eventually joined up as one of the three families of the Mantis during the 11th century, but at present they're still independent. They're somewhat isolated and insular so getting them to agree to it might be difficult, but the fact that the founder of the Catfish is female, and has been doing her best to improve the situation of women (somewhat, it can be spun that way anyway) might help a great deal.
The Moshi Family's whole schtick is a significant adherence to Amaterasu, and once the Mantis were a Major Clan they were the foundation of the Thunder Magics that they got. Well, that and the whole blessing of the mortal Thunder dragon on the whole clan, but still!
Besides the Centipede Clan, the only other minor clan that might have something of a glut of Shugenja that I can think of off of the top of my head is the Fox Clan. By virtue of geographic necessity the Fox have a great many shugenja. The Kitsune Mori is neither forgiving nor terribly mundane.
Sadly, no Salamander or Raven Clans, or else I'd say jump on those options with both feet.