Bruce Upholstery...
Bruce Upholstery (google it) based in London, recommended by Fritz Hansen, will do the Swan and Egg in Fabric or leather. Leather supplied by Andrew Muirhead of Glasgow.

I'm currently having my Swan re-upholstered in leather. Anne's super helpful and nice, you'd need to get the chair to them. It's a very difficult chair to do, many are reluctant to touch it, you get what you pay for, but be warned- it's not cheap, not by any means- even for the swan and I'd imagine the Egg is significantly more.