Here's the straightforward answer:
(e.g., "Ultralinx Wallpapers," "Abstract Packs," "Gradient Packs") on Gumroad and other marketplaces. He rarely offers his full premium packs for free.
It looks like you're searching for free wallpapers from (also known as Oliur Rahman/ULTRALINX), who is a well-known creator of premium design resources, including wallpapers.