I don't know about you, but I was pretty annoyed that there weren't any places in the Commonwealth to buy ammunition for the Handmade Assault Rifle.  Now there are!  You can purchase 7.62 ammo (as well as ammunition for the Acid Soaker and Paddle Ball) from Wolfgang (outside Drumlin Diner, if you didn't kill him), Myrna (Commonwealth Surplus, Diamond City), Rufus (Hotel Rexford, Goodneighbor), Lucas Miller (Bunker Hill, Wandering Caravan Trader; use a Trading Post in your settlements to bring him in) and Cricket (Bunker Hill, outside Vault 81 or outside of Diamond City).

Update 9/12

I added Nuka Nuke, Acid Soaker and Paddle Ball ammo at those same vendors.  For some reason Cricket is the only weapon store ammo seller to have all of the NW ammunition, despite the fact that KL-E-O and Arturo use the same ammo file, so, beats me.  If KL-E-O and Arturo have this stuff for you, consider it a bonus.