Clear PC
http://www.clearpc.ca/ use
3/16" thick Cast Clear Lucite®, (Acrylic)
they have a distributor in France
http://www.textorm.com/pr_trcase.html but if U really want to spend more money for the pleasure - it sounds like U are a Real Modder

so hav a look at the numerous "Clear PC build guides on the web" first
One I like is the
http://www.bit-tech.net/article/72/
http://www.bit-tech.net/article/67/ this case is made of Plexiglas G, cell cast acrylic.
Lexan® is fairly expensive so Lucite (for a case would be better)
I had a quick look in the UK but still expensive
http://www.diyplastics.com/perspexplexiglassprices.htm
Have you tried a Local "Do It Yourself store" we call em B&Q, Do it all over-here they usually stock acrylic in various thicknesses
I'vve gotta go to work now! so I'll be back, to finish my reply
The Tube, Bends, etc is proving more difficult for me to find too
My ongoing quest also

Mat (OOhh thnx for the welcome)