'ebonised' moller chairs  

BJ, You can order your Danish cord and nails from this supplier in the UK if you can't find anyone in Belgium. http://www.marshallmcgurk.com/SitUpon/danishcord.htm
I have recorded many Moller chairs. You will get quicker at it with experience, I think my first chair took about 8 hours to complete.
It helps if you have an original corded chair as a referance, seeing as you have the flat ribbon style seat it may be difficult to get going. I would recommend you buy a book like the Caners Handbook to give you some pointers.
There is also a thread on here related to all things Danish Cord, I think someone posted the link to a step by step video which should be very handy, try searching the forum.

Thanks Moon! I'll look...
Thanks Moon! I'll look further into it.

here is the thread
Great information for those with patience.
No longer would i hesitate to purchase chairs needing
repair though. Very generous help. And you should find
the materials you need.
http://www.designaddict.com/design_addict/forums/index.cfm/fuseaction/th...

Very helpfull.
Would anyone...
Very helpfull.
Would anyone know how the vinyl/leather seats are done?
I would like to see how it's done at the corners of the seats.

I just redid a vinyl seat on ...
I just redid a vinyl seat on one of these chairs a few weeks ago. I would recommend that you do leather rather than vinyl if you have a choice because vinyl is actually harder to work with. It tears much more easily than leather and can't be stretched more than a tiny bit.
Anyway--cut the new piece big enough so that you can wrap it around to the inside of the rails PLUS enough extra to grip--say 2-3" extra.
Notch out for the corners, leaving about 1/2" to 1" extra to fold under.
Staple or tack at center back, then pull taut and staple/tack to center front. Repeat for sides. Then work your way towards each corner. When you get close, determine exactly where you will need to fold under around the leg posts, then carefully cut small slits in the curve to within about 1/8" of the fold. This will allow the folded portion to fan out and lie flat when you tuck it under.
Do the slits only around the post, not on the portion that will lie alongside the length of the leg.
Do some practice pieces with scraps if you want to be sure of what you're doing before cutting into the real seat material. You can also use the old seat covering as a pattern if you have it, but do cut your new piece bigger to start.