After chatting to some vegan friends I have discovered that you can get artificial feathers. I had no idea that there was such a thing! Although stopping the use of feathers in my work is no big concern for me (I'm really happy and relieved that I've chosen to be 100% vegan), it's good to know that there are some good replicas out there that achieve the same feathery effect. They are mainly peacocky feathers and handcut 'duck' type feathers but I think they're really quite effective.
The first picture is an artificial leaf, with fine tendrils & sprayed gold. I think this is really pretty & would work well for some of my large headpieces.
These are from saveoncrafts.com, a US site but I'm sure you can get some in the UK.
I also stumbled on some pretty glittery peacock replica feathers:
This website has a great tutorial on how to make paper feathers. I like this idea though I'm not sure that this would work for my hats. Perhaps tin would be better for me. Hmmmm.
Fake Lady Amherst
This company does a range of artificial Pheasant feathers. I couldn't believe that they were fake at first, but on closer inspection can see that they are polyester. Fantastic!
That's all I could find with a quick Google search, but there's bound to be more. It just goes to show that it is possible to make informed, kinder choices when it comes to craft and design.