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Hello from France !
I can be of little help regarding seeing and manipulating Arca Swiss equipment in real life, except may be if some day I join one of your UK meetings
(I have an Arca Swiss 6x9 F-metric and the 5x4" extension bellows and back, the so-called 'field' 5x4 version), but at least for now I can pass here some useful information.
You can have an idea of the whole Arca Swiss catalogue in continental Europe from various partner vendors & on-line shops.
For example, in Germany,
http://www.arca-shop.de/index.php?language=en
In France,
http://www.magasin-arca-swiss.com/
This French shop
http://www.magasin-arca-swiss.com/ will not deliver to the UK but actually lists
all the official Arca Swiss catalogue.
Including new parts still available from the factory for the discontinued 171 mm system (171 mm cameras, as a whole combination of 171 parts, are discontinued since 2004-2005; some parts are still in stock, but not forever ...),
Reference numbers are important if you look for some second-hand parts; at least you can discuss with people on the basis of real catalogue references.
In France, Mr. Gadat at Le Grand Format shop in Paris
http://www.legrandformat.com/GFweb/GFsommaire.html
is an expert in the Arca Swiss system and he is one of the few European street-shops that actually stocks new and second hand Arca Swiss equipement.
http://www.legrandformat.com/MGWEBOCC.htm
Admitedly, this is of little use to our UK readers

but you can have a look at the above web page to see whether they have the secnd-hand rail or bellows you are looking for.
Just pulling your leg : I actually live in Besançon, 5 minutes drive from Arca Swiss International, and 3 hours by train from the Swiss office in Horgen, near Zurich, so I really do not understand why people pretend that it is difficult to see Arca Swiss products in real life
Not kidding : I'll be happy to give our friends of the UK LF group all the information you would like to know about the Arca Swiss system.
Usual disclaimer: I'm not affiliated with the company, I'm simply a happy Arca Swiss customer ... and close neighbour since about 10 years.
In France the usual way to see and touch Arca Swiss cameras, except of course a visit to the office in Besançon (F) or Horgen (CH) is to attend one of our friendly large format meetings, where Sinar owners meet Arca Swiss owners and peacefully discuss (could you believe this ?)
Example : the 10x8" Arca Swiss F-line camera, 171 model, at our recent meeting in the Jura (camera owner : Mr. Ossette)
More pictures of this meeting here (sorry, the forum is in French)