I would much appreciate if someone could tell me whether a Sarin report can be generated for fancy cut shapes. And if so, how do you get one (i.e. does the seller of the diamond provide this?)
Yes, you can measure fancy shape stones with a Sarin machine. It's a little bit more difficult to analyze the results but the AGA cut system works pretty well for the shapes that are included.
Many, perhaps most, gem dealers have access to someone with a Sarin machine if they don't own one. Ask the person selling the stone to get you a report. They should probably be able to come up with one in fairly short order although they may need to pay for it (and consequently want to charge you). Ask 'em.