How about a gift the party might receive from some monks after a good ol’ fashioned training montage?
Monastic Signet Ring
Ring, very rare (requires attunement)
Given to the worthy, who while not part of an order, have earned the orders respect through effort and training. While wearing this ring, your melee unarmed attacks do damage equal to a monk of 1/2 your level, minimum 1. Also, three times per day, you make a free action unarmed melee attack. This ability returns after a long rest.