An offshoot of the Bifrost, run by Nicolae and assisted by Cresento (reversed from their usual arrangement) selling the rarer reagents and recipes. Need one of those Iron Jaws for a Treehouse Formula? No problem, just 5 million a pop! Dragon Blood? Pay what you would have for all those caches AND the recipes you'd have needed, and it's yours!
Essentially, it would be the Dernier*Cri of Alchemy.
As far as layout...hmm...back room of the Bifrost, the entrance shot of which would be seen as though the viewer were within said shop themselves. Nicolae probably would have come up with the idea so Cres can have petty vengeance against Brennevin.
Alchem*Mi, prehaps?