Most auto parts stores in Europe has the AlKo jack and wheel assembly for trailers of various capacities. I once bought a couple of the lightweight 1980s style jack and wheel in Sweden for about 40 bucks each. The newer units are heavier duty and of course more expensive.
Here they are on e-bay.

http://www.ebay.com/sch/i.html?_from... eel&_sacat=0

In the USA, Wings And Wheels have the Cobra and AlKo parts which used to be at Williams. Perhaps not everything is in the online catalog, but W+W can be contacted by e-mail and phone.
Jim