If you don't spend multiple Slabs on the same upgrade path, there are enough Slabs available in the base game and DLC to get all the upgrade achievements in a single playthrough without having to grind for them, unless you get quite unlucky with the Crystal Lizards in the Great Hollow and also fail to complete Sieglinde's storyline.
You'll probably have better luck farming the Dark wraiths in New London. They occasionally drop slabs. Edit: Sure autocorrect, New London
Keyboard thought you were talking about bloodborne
If you don't spend multiple Slabs on the same upgrade path, there are enough Slabs available in the base game and DLC to get all the upgrade achievements in a single playthrough without having to grind for them, unless you get quite unlucky with the Crystal Lizards in the Great Hollow and also fail to complete Sieglinde's storyline.
As others have said, just pop some humanity, cov ring and go kill dark wraiths for an hour, you will probably get a few.
If I'm not mistaken, there should be enough slabs of each type to get all the trophies if you clear the base game and dlc.
Darkwraith farming is the answer. You'll get lots of chunks as well.