I played with a modded kingdom where the weaver access is super late game, [Mod] (A20) The Bastioneers! More Dangerous (and Mod-Friendly) Than Ever! Help me test for A20!
All bolts that I got was from enemies drops, no merchant ever sold one. I would noticed if they sold cause I had a lot of items in the queue waiting for bolts…
All that in a14, not played with it in a15 yet.
Edit: from jomaxro reply I guess the mod changed the trades then.