where do i find companion change vendors.. specifically for akarri (spell?) ?

Not sure about Akarri (?) but you will find customizations on Taris, Balmora, Blesavis and Illum as well as Fleet if you have as Security Key or CE.

Locations:

Belsavis: Near where you land: M-5Q5 (1267, 259)

Balmora : Inside one of the buildings near where you land: Gunnta (277, –232)

Taris: Inside the Cantina (-1902, 366)

Fleet: Security Key Vendor – near the Cantina in the middle

CE; Collector’s Edition Vendor – on top of the Cantina

IlumOrb: Ilum Orbital Station Security Key Vendor

Ilum: Sergeant Koam at the Ilum base (513, 635)

(from Dulfy.net - hope that's okay to cut and paste)