In France, you can find organic meat/egg/butter in any decent groceries store (it's organic if "bio". Otherwise, "label rouge" means high standards though not necessarily organic - though by US standard I'm sure it's super-organic). However this does not mean the nutrition is 100% grass-fed, for that I would go around butchers and ask if animals were pasture raised only (élevées en pâturages exclusivement). I don't have any butchers address to give you since I'm usually ok with "just" organic certification when I go there, but Paris is bound to be butcher friendly...

In Europe almost all the meat and milk products come from grassfed cows. They are out in the field for most of the year and during the winter season the are typically fed dried grass/hay. During that time they can be fed some extra foodpellets. All the butter comes from those cows and is typically grassfed :). The egss you buy can come from a variety of places, productionmethods but here in the Netherlands that is pretty well labeled. (although there is a commercial interest to label as green as possible to sell more so a bit of caution is neccesary

ambrews your suspicions are correct. In France almost all beef is grain-finished. Try grass-finishing a Blonde d'Aquitaine!

What Wedzir is pointing out is that French beef is likely to be a culled cow of 4-10 years. That is way older than any US beef. US beef is usually under 2 years of age. In the US, culled cows make hamburger meat. A retired mother cow of 10 years of age has eaten a lot of grass in its life. Still, she'll get a lot of grain to be finished and spent that finishing time in a pen indoors and that messes with the meat pretty quick.

In the US when you get a steak you will likely be getting a steer (castrated male) but in France you will get a fattened retired mother cow. The male calves in France usually go to feedlots in Italy and Spain. They are the premium product but they aren't eaten here in France.

US beef is also mostly feedlot beef where the young animals spend some months in a facility where they are fattened up in large numbers. France has its feedlots up north where you Parisians are. I’m not sure of the percentages but there’s less feedlot beef here than in the USA.

Good luck in your search. If you ever make it to the Southwest you should check out our beef herd.