It probably depends where in Europe you are going ? A great resource to check out is www.davidlebovitz.com -he has a tours link, and you can search chocolate on his site for a variety of information and places . I recently went to London and checked his site for any tips and info (Melt and Borough Market ) they ended up being the best spots to check out . If you will be in Paris his book "Sweet Life in Paris " is a must read for the flight over.
Keep us all posted on what you discover or plan to check out!