Very rare as not many consumers do large amounts of copy work. Labs, institutions etc got them from large suppliers in the past like Ruby and CP or direct from agents.
You could also convert an old enlarger to a copy stand, only you would have to fashion the light fistures if you're using hot lights. lots of clamps and brackets/hot-shoe mounts are also available these days.
I am absolutely not sure, but you could try asking shops like Fee Fee in Chinatown. Even if they don't have, they might know of someone that does. The younger lady there is very helpful. They still take on B&W processing BTW. Alternatively, you could try the 2nd hand shops around the Peninsula Adelphi area. Some of them may still have these 'treasures' hidden away at the back of their stores. Also http://search.ebay.com/search/search.dll?from=R40&_trksid=m37&satitle=Kaiser+copy+stand&category0= At the very worst, if you can't locate one here and don't want to import, it's also something you could DIY.