Minor spoilers concerning all the items that can be used to buff sleight of hand checks.
The ring is hidden on a skeleton by a bush near where the "Paladins of Tyr" are. The gloves are sold in the Zhent hideout, before then there are +1 gloves in the first fight with the goblins. There's also cloth armour dex +2 and advantage sold by the merchant at the start of the mountain pass and a ring of dexterity 18 sold by the gith merchant. If you aren't using a cleric or druid for guidance there's an amulet that grants guidance on top of a hill just outside the druid enclave.