Where is the Vastaya onthe map ??

Vastayans live dispersed. For now we know nothing about well defined territories owned by vastayan societies.

There are some underwater, but most are somewhere in or around Ionia.

They are everywhere around Ionia and some are underwater..

Namis people are next to Targon, Rengars are at the borders of Shurima and Kumungu Jungles, Ahri originates from North part of ionia, Wukong is on the Island near Wuju (but his people are on the Southern Islands.

vastaya are a race that is all over runeterra.

Rengar lives in shurima(likely the big jungle area next to it),Nami lives somewhere close to targon and Wukong,Xayah,Rakan and Ahri live in ionia.