If you go to Morrisons or Sainsburys to the dried veg section you can get bags of dried seed mix to make soup with. Like scotch broth or one with pasta bits in it. Our hammies love this. Just don't get one with dried onion or leek in it.
We breed and show and know most of the UK breeders and by far the majority use Harry and regard it highly. Most people supplement it though. We have never had tummy trouble using Harry. That said there are other brands out there so you can try out some and see what your hams like. Just make sure you do gradual changes so the tummy adjusts.