are there srsly no vendors that sell them

You can find bowling balls at the bowling alley; that place that's ran by Mr.Handy robots (someone help me out with the name)

so i can use bowling balls as ammo?

Why not? and what are cannon ball use for?

Broadsider

You can use really anything in the Junk Jet. Bowling balls in the Junk Jet are just fun to mess with.

no i need ammo for the broadsider

You can buy from diamond city after certain level. I think after level 20 or 30. I use boardsider all the time, the guy vendor sell about 5-8 cannon balls and the one next door sell 0-4

I always restock every time I see they on sell.

thank you