From Pathfinder Lost Omens Firebrands, which isn't enabled.

Shield Pistol

ITEM 0

UNCOMMON ATTACHED-TO-SHIELD CONCUSSIVE FATAL-D8

Price 6 gp

Usage held in 1 hand

Bulk 1

Category simple

Group firearm

Damage 1d4 piercing

Range 20 ft.

Reload 1

These unique firearms are designed to attach to shields while still firing normally. Shield pistols are popular among Firebrands in the Shackles as they allow them to hold a blade and a firearm in each hand without giving up on defense. As is normal with firearms, a character doesn't have access to shield pistols unless they separately have access to firearms.

Pathfinder Lost Omens FirebrandsOGL