Welcome, welcome!!! I'm new to this too, but I can assure you that the people are great and you'll have a lot of fun and empty pockets.
As far as where to find cels, I'd check ebay, or yahoo japan. Most sellers on YJ will not ship overseas, but you can hire a deputy service. There's a whole list of them on
http://www.rubberslug.com/resource/links.aspx
Plus that link has links to a lot of other information about different types of cels, where to buy cel books, etc. It's really informative. If you ever have any questions about cel preservation, just ask Roy (points to above post); he's the resident expert.
Another site you might try is www.cels.org
They have a lot of links to different online stores, though some of them are dead. I think that site has a link to an online store based in France that takes Euros. That might be a good bet for you.
So you're from the Netherlands, huh? Well, just to let you know, I've been informed that my nickname is a naughty word in Dutch. Well, I've had friends calling me that for a while, and Dutch is not one of the languages that I speak, so it doesn't bother me. But I'm sorry if it offends you. I don't mean it to do so;)