
I don't know anywhere that makes them for small dogs, but you could try contacting Culpeppers to see if they are able to make some custom booties for you.
http://www.culpeppers.co.uk/catalogue/?cat=booties. They make custom leads etc so will probably be able to make boots up as well.
Failing that you could quite easily make some fleece booties which will be fine to stop the snow balling up in his feet. Stretchy velcro is best to secure them at the top if you can get it.
When you first put them on him, he will probably not want to put his feet on the ground, but they soon get used to them. It's very funny to watch, though.