Oh my! Thank you everyone so much for your in depth and thoughtful responses.
That is such an intelligent way to go about it, and I cant believe i didn't read that part about how they do it!
@mikesc I would never duplicate their product for resale. I only wanted to make one set for myself as they don't have the colour I need to match the rest of my bike.
I dont think ill be learning to lathe any time soon, so I guess ill just have to live without them for now. Maybe, just maybe I could fill a standard rubber fork gaiter with plaster and cut the rubber from around it to give me a mold.
Thanks all again, I really appreciate your help.
Cheers,
Simon