Id like to ask what would be the source of horses used in war by french heavy cavalry in a timespan of about 1420-1600. Would they be imported or would there be good horses bred in France itself? Were such a centers of horse breeding widespread or would there be few of them exporting horses to wide areas around? Would a noble able to afford it employ his own horsebreeders/horsetrainers?

Have a nice day and thak you for your answers :)

Hmm. Ann Hyland's books come to mind. I also get the vague recollection that one of Anne Curry's books has some material on horse supply in the Hundred Years' War, but I don't exactly remember which one. You probably should try pestering the folks working on this blog:

http://horseinculture.blogspot.com/

Stay right away from anything written by Hyland. Every sentence she writes has the subtext...
"aren't oriental horses wonderful compared to those nasty European ones."
On top of that she doesn't have the faintest clue about medieval warfare. Andrew Ayton or Phil Sidnell would be better sources.