Vorinism is mostly practice in the 5 Vorin Kingdoms ( Alethkar, Jah Keved, Kharbranth, New Natanan and Thaylenah) all located on Eastern Roshar. So it is propably from there.
Also Vorinism was probably spread in this 5 kingdoms by the Hierocracy since it wanted to unify Roshar in Vorin faith. However I don't think Vorinism spread too much afterward since the ardentia lost a lot of power after the fall of the Hierocracy.