Item changes that came with the patch 9.0.4 is currently work in progress. You can track latest changes on the wiki through the Recent Changes page.
Heavy Leather Set is the armor set that comes after Leather Set in Rise Online World. The next grade is Plate Set.
They can be dropped from various creatures in Dorion, and are also sold as +1 by Armor Merchant NPCs, Marcus, Margus ve Thalia.
Crafted (and Enhanced) versions of them can be crafted with Tailoring life skill.