I think Ade's one is from Warco, and is similar to the ones you see all over eBay, etc.
I've been looking at the topic a little myself, as I'm not really keen on buying a small mill that I will still want to upgrade in any case. There seem to be three routes:
Bodge: I was considering simply bolting an angle plate to my cross-slide, and my compound to that. Unfortunately my compound has a fairly fixed post in the middle of it, the removal of which would be more of a pest than I think it's worth. Acquiring a surplus compound from eBay or the like would seem to make sense, but people want surprising amounts of money for them.
Buy: there are quite a lot of not very good devices out there, all of which I'd need to make an adapter plate for. Obviously a vertical slide is a compromise but I kind of feel all these are a compromise too far.
Build: there have been (at least) two builds in MEW, one recently in 305 and 306, and a bigger, more robust one in 205/6/7. I haven't had a proper look at this last one but just from scanning it looks like a solid machine. I was thinking of modelling it up in OnShape to see how it looks. Other suggestions warmly welcomed!