I know it's just these three, and getting someone else would mean getting another person into the scheme, but it seems like a short-sighted idea to just source directly from the suppliers like this. In a world that apparently doesn't give a damn about copyright, it would be very easy for a merchant company to ask around and find out what they're buying and then duplicate the product (which I'm assuming the bigwig merchant at the end there's gonna do). If there was a secret to the manufacturing, that'd be one thing, but it's literally just mixing the two powders they're buying into the potions they're also buying. Once they confirm the effect, it's just trial+error to get the right concentrations, at which point any large merchant company would be able to strongarm MC's crew out of the picture.