UPDATE 9/4/19: The Spikels Max Pose has been found While searching on the wiki I found some merchandise with some of the 2014 maxes on it.
They actually have action poses just like every mixel from series 1-3 had
Also on the canada website for CN the Fang Gang Max appeared with an action pose as well
Frosticons Max, ECA host mix, and the Murp from Murp (lol)
Fang Gang Max on the canada mixels website
GCM On the Mixels facebook? idk
Cragsters Max seen on this art kit
Some Maxes that don't have artwork or haven't been seen
Infernites Max
Electroids Max
Flexers Max
Credit to CoinsCP for finding this.
Wiztastics Max
who knows, maybe we'll find more lost media stuff