There is also www.modelguncollector.co.uk which are more modern although there are a couple that could be viewed as historic in a certain light.

Other than this company, I am afraid you will be looking at importing from Japan. It is still possible even with the new gun laws. Just ship them in pieces and make the kit up yourself. There is a model gun discussion group that I joined when I was looking into these type of guns for LARP but I can't for the life of me remember what it was called. (probably had the words model, gun  and forum in there in some format). If you google it, you should come up with an answer. They may be able to help more.