Have you finished the Bad Borken part of the main story yet? iirc, you need to meet and talk to him in a couple different places first, finish that part of the main story, and then his shop should open in the place I mentioned in my previous post.
This makes me wonder if, once the game is fully complete, someone will make a complete guide to the game including sidequest trigger conditions, the results of the various choices throughout, and optional missables. For the latter, the fortune teller’s shop in the Capital helps a lot for all the important missable things, but there still are a few small inconsequential ones like a bonus level up for Clara I missed the first time around.