Swindrik can be found hanging out on the east side of the Dueling Weapons/Armoury Limited shop in Trinsic, as shown below:

He tells the player to ask about mandrake root at the Folley Tavern in Paws. However, nobody at the Folley Tavern seems to know anything about mandrake root. I haven't been able to find an explanation for this online.

What gives? Is he full of it?

Edit

Apparently I should be able to ask Greg or Rob about it, but the only thing I am able to ask them about is food or ale:

At this point, the game only accepts "A" or "F" as input. After paying, he asks "Somethin' else?" to which the player can respond "Y" or "N". Then the conversation repeats.