Your best bet is try placing a wanted advert in the classifieds here.
There were once a lot of professional darkrooms in most UK towns & cities, many would have had a dry mounting press, so ask around. For instance where I lived in the UK there were at least 4 factories with their own photographic departments, and 2 newspapers. I got mine from a newspapers darkroom about 35 years ago, when the two papers merged.
I may have an article on how to make one, I'll try & find it next time I'm in the UK. Even a broken press is worth buying (as long as it's just the electrics broken). Modern heater pads are a lot better than the old elements they used to use and far easier to fit.
Ian