I give between 12 and 15g of milk kefir grains in exchange for a bottle of pasteurized or microfiltered organic milk.
My grains are fed with organic milk (cow and goat).
I also provide a practical sheet explaining the methodology for those who are getting started.
To pick up on site (Paris 14th : Plaisance metro station nearby) in the evening (Mondays, Wednesday, and Thursday evening) and possible some weekends.