there are some sites in Europe, but not as much as in the US. There several people selling Airstreams in the UK and in Germany and there is also an Airstream Forum in Germany, but its very, very quiet in there...
People selling Airstreams in the UK are:
very nice people in Germany, who sell europewide if wanted and have one of the best pages in Germany (I am not related to this or one of the other sites in any kind, but this one is a great resurce for information): http://www.campingoldtimer.de/
They also guide you to other Airstream Sites in Germany where you can rent Airstreams for Events etc.
An other very nice site is a mobile Cocktailbar :
The German Forum is available under:
If your friends want they can also contact me (firstname.lastname@example.org
) , I am new to Airstreaming (hopefully will buy one in the next few weeks), but Airstream(er)s are rare over here...