So, you are allergic to leather? I have never heard that before. Anyway you have some good sources here, and if you can't find a source to buy from, some Tailor shops can remove the leather band and replace it with a silk one.
As to allergies to leather bands; it is usually not an allergy to leather, but a hygiene thing. Keep the band clean from sweat/salt and dirt and it shouldn't be a problem.