Where can I find them and how many are there?

I was in one on the rue de Rivoli.

Go to www.hm.com. When you choose the country, choose France or Spain. If you don't speak French or Spanish, the link you want will be at the top of the screen, second from the right (in French, Nos Magasins). Then you want the middle drop down list. There are tons of H&M's in France, and eight in Paris. All addresses are on the website.

the corporate website, www.hm.com has a listing of all stores in paris

Nine in Barcelona, to answer your other question.