Upholster swan chair  

Give this a whirl
Check out http://www.bruceupholstery.co.uk/page3.html
They are recommended by Fritz Hansen, very highly none the less. They are it would seem, very good and very nice to talk to on the phone. I was pleasantly surprised at the cost too.

one thing....
One thing I should have mentioned is that while I didn't think the price was too bad, for the work involved and what is a complex piece to cover, it's alot more involved than you might imagine.
When the material is removed, the foam usually comes with it as it is bonded. This means that they will replace all of the foam on the chair too, essentially just stripping it down to the fibre glass shell.
I was told that two metres of material is needed, I'm not sure what this equates too in leather skins.
The chair really does warrant being done properly, I have the fritz hansen version in fabric. I'd love a vintage leather one. Either way, best of luck, I'm not sure what you paid for the chair, but I suspect that if you are wanting it re-upholstered in leather, you are looking at many times the cost of the shell.
I do know that the originals are draped with the wet skins hence they form the shape of the chair, I guess this is more costly to do, not only from a raw materials point of view.