LFS usually won't take fry, but after they reach an inch, you might be able to find them a home. I keep live bearers in tanks with lots of cover for the fry. Rocks, shells, and java moss all help with the survival rate.
This is going to be an on going problem if you keep these fish....it seems heartless, but out of all the molly babies I have had I've only sold 5 of them....Most go over into my 125 tank. In there I have had 7 grow up to adult size....most get eaten by my nocturnal predators.....Black Ghost knife, and Raphael cat......I have even seen the two rainbows eat fry....The only long term solution is to get rid of the live bearers...if you don't have room, or don't feed them to other fish...