You get them through the repeatable stone statue quest in the woods. The slave you get from successes and critical successes can have tigerkin body parts and possibly be fully tigerkin. I also believe that gifting them to the cat tribal nation afterwards has a way of creating more but I've never gone that far down that questline to find out. The gifting event happens automatically after you have a slave from the statue event although it usually takes months and even years to trigger.