He used dense cross-hatching and textures to create a "mosaic" feel.

There are archives—Internet Archive, specific comic hubs (like GetComics or ComicPiracy—we won't link them here) where users have scanned the old NBM editions from the 1980s and 90s.

However, I think you might be referring to a specific PDF related to Sergio Toppi's work. After conducting a search, I found that Sergio Toppi has worked on several notable projects, including:

that offer high-resolution viewing of his intricate linework. Original Art Galleries : Sites like 2DGalleries

If you are looking for specific volumes to download or purchase, these are highly rated: The Collected Toppi Vol. 1: The Enchanted World Book Review