Have you thought about making your own? You don't have to be particularly talented. I'm not, but DS and I still managed to make a couple of pretty-enough mobiles at a workshop at school. We used garden wire (I think) and invisible thread of some sort, and experimented to get the right balance so that our "kinetic sculptures" moved nicely. I suppose wire might be a bit scary if you're thinking about hanging it over a baby's cot but I'm sure you could come up with an alternative.
Or what about Etsy? I did a quick search. Lots of inspiration if you do decide to make your own and lots of lovely finds if you prefer to buy.
Don't know about mobiles but lovely baby toys and clothes on the Beandrops website at www.beandrops.co.uk and they have a 10% discount on all orders placed before 31st August. They have lovely nursery prints too.
We found the most gorgeous little toy shop in Minehead when we were down that way on holiday, owned by the friendliest, loveliest, most helpful man. They have some mobiles, and some wonderful traditional toys here