Best I've come up with so far is that there's such limited quantities it's kept under much more security than usual because it's essentially being grown for a Count a few worlds away and he would be very miffed his private stock necessary for *his* illness was being given away.  (Counts are at the level of my PCs parents.)  Not got much further than that but essentially I'm looking for something that doesn't necessarily directly utilize their money, but does utilize their high social standing.  Is 'fixable' within a day or two so we can do the rest of the adventure rather than get completely sidetracked (although I'm open to that as well!).  And perhaps leaves them with a potential Enemy for future adventures after this one.