[FairyKing]

Based on the Vistamps that were shown to exist in unpurified forms (i.e. only used by Deadmans so they have no rider motif) and how the animal's appearance could be adapted to a Rider's aesthetic, I'd go with:

Geats - Cheetah (upward ears and pointy snout, spots on torso as the "bullets" on Geats's chestplate)
Gotchard - Smilodon (mouth open with eyes as the "goggles" and saber teeth as Gotchard's actual arrow-eyes)
Gavv - Koala (rounded ears as the head crests and pouch as the gavv mouth, with the demon riding in the pouch like a baby koala as the Gochizou)
Zeztz - Rafflesia (large petal as the smooth face and flower opening on the chest as the Zeztz Driver)