To craft any spell, you must be a Legendary crafter.
That means, you must quest all the way through Celestia and into the first few quests of Zafaria, then complete the crafting quest for Ghostmane. It will require a lot of aether, fossils and sunstone reagents, for you have to make two Conga drums and use them to make two Spiritcaller drums. (The Conga drum recipe is available in Celestia).
Once you are a Legendary crafter, there are two locations where you can purchase the recipes to craft spells.
The first one is located in Mooshu. You must complete the Shirataki Temple dungeon and battle the final boss in that instance before you will see the spell craft vendor. If you ever want to go back, you'll have to do the whole dungeon again.
All but one of his spells cost $60,000 gold just to buy the recipe, so have your gold ready before you start the Shirataki Temple dungeon.
The other spell crafting vendor is in Avalon. You must defeat the boss in the Dun Scaith tower in order to find Grady. If you don't have access to Dun Scaith yet, you can port in to friend, but keep in mind YOU must be in the battle to defeat the boss or else Grady will not appear to you.
That depends on the spell you are wanting to craft. There are spells to purchase in MooShoo and Avalong for example from vendors. They do not include quests specifically for the vendor but you need to be at a certain point before you see the vendor or have access to the areas they are "hidden" in. Each are behind sigils. What spell(s) are you wanting to craft?