Rippled Sycamore is by far the most common decoratively figured timber that you'll find in the UK. Hang around enough timber yards and before too long you'll find some and as often as not at standard Sycamore prices to boot.
But if that's not possible then try calling Timberline,
Both regularly have Rippled Sycamore and both offer a mail order service.
Figured Maple is more of a North American thing, you do find it in this country, but because there's an established musical instrument market for Fiddleback maple or Quilted Maple then the prices tend to be quite a bit higher.
Finally, if you don't need much and if you're in the New Forest area then drop me a PM, I specialise in furniture making with highly figured timber, so there's normally some Rippled Sycamore or figured Maple in the off-cuts pile.