Hi Izzie
Sorry, I don't live in Europe, but I think I can help you.
If you want authentic cast autographs, the best way is to write to each cast member
individually.
In your letter, include a brief introduction of yourself, say what you like about the person's work, politely ask for an autographed photo and thank them for their time.
When you send your letter to the specific cast member, remember to include a self addressed envelope (it's best to send one of the large 9x12 ones) with some International Reply Coupons (for a 9x12 envelope, at least 2 will be sufficient.)
For example, if you specifically wanted Ellen Pompeo's (Dr. Meredith Grey's) autograph, you would write a letter to her and include a self addressed envelope and International Reply Coupons with your request. Include all of this in the envelope addressed to Ellen Pompeo, stick enough stamps on the envelope and send it off
However, if you just want a picture of the whole cast (it'll be a preprint though,) you should write a letter addressing the whole cast to the production office. Don't forget to send your self addressed envelope and IRC's with the request though! An address for Grey's Anatomy can be found
here.
Good luck!
nowandagain [rockon]