Though here are some booking agents:

http://www.waderson.com/ (has stalking in Scotland)

The Hunting Consortium, hunt@huntcon.com

Diana (though its Danish)
http://www.diana.dk/diana_jagt/html/

I've not actually used any of these services I've just looked into them.

At the risk of sounding controversal, for many areas in Western Europe I'm not sure you really need a booking agent. I am sure of their benefits when hunting Africa, Asia, or Eastern Europe/Russia. If you look at the prices of say red deer stalking in Scotland and compare the standard prices estates or stalkers charge compared to what US based booking agents normaly charge I'm not sure most booking agents are worth it. The few times I've hunted in Europe I've just booked like a local would and had a great time for a good price.

If you are interested in the UK buy a copy of "The William Evans Good Shoot Guide" sort of like a British "Black's Wing and Clay" has contact information for agents for game shooting and deer stalking.

Hope this helps! Hunting in Europe is great fun, and it easy to fit in things for the familly so it reduces hunting stress