Do you know Julio Sillet? He's making Free 3d and Blender content for everyone.
He hasn't a website but Julio is using Gumroad and Patreon to share his creations.
He wants to reach 1000 textures in time and maybe we can help him with this goal.
You can support him and get some rewards. He is sharing SBSAR & SBS files for his Tier 3 patrons and it's a big opportunity if you want to adjust textures as you want.
SBS are files from substance designer, with these you see how the materials are done procedurally and create your own materials from those.
SBSAR is a substance file that you can open with Substance Player(Free) so you can export the size and format you need. The advantage of there is that they are very light (100kb) and from these, you can export even 4k.
Visit Julio's Gumroad page and download free pbr textures