I am attempting to create a magic item and cannot seem to find Thorn Whip as an available spell to attach to the item. Under the 'Add a Spell' section Thorn Whip is not available. I am trying to attach the cantrip to a suit of studded leather armor. Unsure what other information you may need.

Thorn Whip was never published for free, only as part of the paid content included in the PHB. You will not be able to attach it to any homebrew unless you have either purchased that book from a his website, or at least that spell from the book.

Thank you, thought all the Player's Handbook information was included. OOPS.

Quote from theHumanChris >>

Thank you, thought all the Player's Handbook information was included. OOPS.

 Nope. Everything from the Basic Rules & SRD is included, but that doesn’t include everything from the PHB.