7 species have Shell Armor as a hidden ability, 18 as a normal one

Effect, in PokéAPI's words

“Protects against critical hits.”

As a hidden ability

Species	Slot	Note
Torkoal	Hidden	Since Generation V
Turtwig	Hidden	Since Generation V
Grotle	Hidden	Since Generation V
Torterra	Hidden	Since Generation V
Oshawott	Hidden
Dewott	Hidden
Samurott	Hidden

As a normal ability

Species	Slot	Note
Shellder	Normal
Cloyster	Normal
Krabby	Normal
Kingler	Normal
Lapras	Normal
Omanyte	Normal
Omastar	Normal
Corphish	Normal
Crawdaunt	Normal
Clamperl	Normal
Dwebble	Normal
Crustle	Normal
Escavalier	Normal
Shelmet	Normal
Turtonator	Normal
Chewtle	Normal
Drednaw	Normal
Klawf	Normal

Elsewhere in PokéAPI

7 more holders without a page here

Alternate forms and other species that PokéAPI lists with Shell Armor.

Slowbro Mega, Kingler Gmax, Lapras Gmax, Drednaw Gmax, Sliggoo Hisui, Goodra Hisui, Scolipede Mega