Search Q&A
Kefir live culture
I saw them for sale in Amazon UK (some months ago though) .
But there are also some Facebook groups in Brussels where people are willing to donate them for free. Try "Expats in Brussels" and do a search by "kefir".
Carrefour sells Kefir. Can't vouch for the quality though.
Carrefour (or many bio shops where I tried) does not sell Kefir grains which is what the original poster is looking for. ("...live culture...").
Kefir related products can be found in Carrefour and other supermarkets.