The various Transmute recipes are scattered throughout the Spiral with each of the Crafting Quest givers. OR, if you have access to Celestia Base Camp, go see Avery Templeton near the entrance to the Survey Camp.
As an additional note, you generally have to complete the crafting quest with a particular NPC and moved on to the next one before you can buy their transmute recipes. For example, if you have finished the Wizard City crafting quests and gone to talk to the Krok crafting teacher, then go back to Wizard City to check for the transmute recipes at that time. You should find them available then. Just keep tabbing over on the recipes that they offer.