My local feed shops/pet shops always have lots of sample bags available so would recommend you visit a few and see what they have on offer. You can always try adding either just hot water (seems to make it smell better) or some hot Bovril to see if that tempts them to eat.
James Wellbeloved website sends you samples of whatever you ask them to. I am thinking about changing my pup's diet so looking around at the moment. They do different flavoured kibble.