Yep, Helium rich gas giants are about as rare as it comes. However, if you find one in a system then there may well be others. That's because the gas giant helium percentage is the same for all gas giants in a system (I guess the stellar forge can be forgiven some simplifications). If the percentage is above a certain amount then class I giants are reclassified as helium rich.
cheers never seen any since then incidentally Allitnil i am sitting in a system with your tag on the main star right now lol.