There are glyphs for standard Pthumeru Ihyll, Lower Loran, and Great Isz which grant you Blood Rocks, all on the first layer pre-dungeons.
Their glyphs are as follows:
- Pthumeru Ihyll - jrwffkyp
- Great Isz - rpzkeauc
- Lower Loran - 6rxwxu3e
These Blood Rocks can only be obtained once per dungeon type (Pthumeru, Loran, and Isz). That is, if you obtain a Blood Rock from Pthumeru Iyhll above, no other Pthumeru chalice will yield a Blood Rock in a chest. It will instead be replaced with Great One's Wisdom.
This means you can only get three Blood Rocks within the chalice dungeons, but this excludes drops from bosses. The last boss of any depth 5 chalice has a small chance of dropping a Blood Rock, but the only limiting factor here is luck; you can farm these bosses for Blood Rocks until your heart's content (or your patience runs out)!