I came across this site while looking for something else and thought I would share. Custom Printed M&MS
It's based in the US but does have a number you can call to enquire about shipping internationally.
You can choose from a heap of different colors and then personalise it how ever you like! One side has a picture of the bride and groom on it and the other side has text. You can also make them with text on both side rather than a picture. They make great favors.
Even if custom printed M&Ms are out of your price range, they do have some pretty cool ideas on how to decorate cakes with M&Ms so check out their page.