Try a proper saddler as they should be able to source one for you. By proper I mean someone like Gibsons of Newmarket (who could well have them in anyway as some racehorses use them) not something like Robinsons.
Very gentle very hard wearing. I have made one by wrapping a rubber bendy bit in chamois leather, but I need one that is a bit more competition legal. Not the Sprenger one in this case.