Stones for the garden (Brussels)

Hello,
I have a little garden and was hoping to arrange it a bit for spring. I wanted to make a little terrace by putting irregular stones. Is easier, because if I want to put wood I have to make the terrain regualr, which I think is completely impossible in my garden. The stones I am talking about are not like the square ones that fit together like pavement ("dalles"), but relaly irregular ones that you just throw there. They come in big bags. I saw threy have some in OhGreen shops, but I didnt see them in Brico. I would like to know two things:
- Does nayone know where can I buy them apart from OhGreen?
- Can anyone maybe tell me more or less how many bags of these stones you need to cover 1m^2?
Thank you very much