The Meyer Hatchery in Polk Ohio just started selling BCMs. Or you could buy some hatching eggs from ebay or a breeder........I have one BCM pullet, but no rooster......her eggs are super dark brown. She's pretty too.
Look on Craigslist - Plenty of people sell their chicks there. Otherwise, if you can't find anything local you'll just have to go with eggs. Nothing wrong with that - Infact I like it a lot better. Almost all of my Marans are in egg form in the incubator right now, and I'm getting much better odds that way. (get to see the egg, it is often cheaper, etc.)
Marans aren't like RIR's though - You can't just ask for and expect someone to have run of the mill stuff - People who breed Marans are usually dedicted to make "solid gold."
. . . (except hatcheries, but they don't really "breed" stuff, they just let things take their course en mass and sell. . .)
eggbid.com has had some BCM but thats all I know about them. I have some coming from chicken scratch poultry in April. Check out black copper marans and egg color on here there is a huge thread going and several sources of at least eggs good luck I'm having trouble waiting til April myself.
If you want them for their nice dark egg color, you will probably be disappointed with the egg color. I know that's the case with hatchery cuckoo Marans. Like several people have said, You are better off buying from a good breeder on BYC or a member of one of the Marans clubs.
OH so true ... ! I have 3 different hatches here at the house ... and the one form a club VP are no where close to the ones I drove a picked up! Its so much better to drive and look at the chicks ... or the eggs ... before you buy ... Not everything you see on line is what you get!