Here's what I'm thinking: The brothel staff would surely force this magic-quelling ingredient on everyone, right? However, even they have their shortages. We'll say that they prioritize on those who perform offensive magic, but are a little bit skimpier on other mages, hence why Rebecca still has her seemingly-harmless telekinesis. Also, we'll say that Hatiith's cane does have some arcane possibility since he doesn't have any brawn to him anyways, probably enough for one solid spell on Jade or Xerlai's part in their current conditions. It's definitely farfetched, but I think we can all agree sparing a few details about a ship that's currently hopelessly on fire isn't too scandalous story-wise. Rebecca can definitely keep the money, it's on me for giving you all nothing to go off of in the canteen.