I can find unique weapons at a few vendors, I can find crossbows that look like they were forged in the flames of hell, but I would gladly pay their prices of coin for a single shovel. I can't seem to find a single vendor that sells one!

Anyone know characters that commonly sell them?

never seen a shovel sold.. but you can pick them up .. for example at the first teleport portal in the game bit to left

Or there's one in the graveyard in Cyseal over to the right hand side.

Another one can be found in the cellar of Esmeraldas shop. Inside the "secret" room by the bookcase.

Plenty to be found in Cyseal's graveyard, too. Just wander around with ALT held down.