Back in 4th, the Fox clan was a staple minor clan (or branch of the Mantis) and available from in the 4th edition core book.
When 5E came around, they revamped the whole character creation process, and slimmed down the possible options: The 5e core rules only contain great clan families and clans as choices, but at least mentions the Fox-clan when showing off all the minor clans on page 18.
Emerald Empire brings the imperial families and a Kitsune Impersonator school, but that is for Fox-spirits, not human members of the Fox-clan lead by the Kitsune-family. While the latter happens to have Kitsune-spirit members and descendants, this is not a class for the normal Fox-clan.
Path of the Waves describes a little bit on the fox clan lands and an example monster for both a mundane fox and a trio of Kitsune-Spirits as an encounter, but no explicit rules for making members of the Fox-clan.
Shadowlands has the minor Falcon-clan and its Toritaka-family & -dojo... but no Kitsune here either.
Courts of Stone brings (according to the wiki) the minor Deer-clan and its Shika-family, but again, no Fox.
Celestial Realms delivers allegedly the Centipede-clan and the associated family and school.
Which book do I overlook that hides the minor fox-clan and its families or might it not have found publication yet?