i live in belgium but I don't know in which shop I need to go , I there a site so I can see it
btw it's also possible that the don't do it in my coutry , whe never heard from it before
It looks like there are details on the official site. Either here for French Belgium or here for Dutch Belgian.
However, the translation in Chrome just says "participating stores" so maybe it doesn't actually say which stores on there. It is very likely to be any large chain of gaming stores in the country (e.g. anywhere you would go to buy games).
It is a little late, but yesterday I found this
According to the Nintendo website it will be possible to download Keldeo in Fnac and Makro stores, this saturday ( 6 october ).
EDIT: The link is broken, but if you go to Nintendo.be, and search 'Keldeo', the article will appear.
The event is for both French and Dutch Belgium.