This should be EULA compliant
The datapack adds 3 weapons, found in chests in structures.
/function can also be used to get them

I can try to make 1.17+ compatible version if someone wants it, but it might not work

Flintlock
-Pillager outposts
-Strongholds
-Weaponsmith houses

Blunderbuss
-sunken ships
-buried treasure

Musket
-Pillager outpost
-Mansion

About items

Flintlock -
Easiest to find. Works well enough.

Musket -
Long range, powerfull and reliable.

Blunderbuss-
5 different ammo items.