Demon boots are no longer available in the UK due to the previous UK importers for Demon retiring and selling their business. The new owners made so many changes and eventually in their "wisdom" decided to brand Demon along with their exisisting lines. It left me with quite a void to fill in my leather boot range as I had been selling Demon boots for almost 20 years and they were always very good value. I have replaced them with Grisport and I have not been at all disappointed. They are a nice wide fit, lightweight, waterproof linings and several models have a Vibram sole unit. Take a look at the Grisport "Avenger" - I am confident this boot will be a suitable replacement for your old Demons.
You should be able to get your Demon boots resoled by a high street shoe repairer but the cost of repair and condition of the upper might make it more sense to buy a new pair.