Reefcentral.com there are a lot of great guys on the Chicagoland Marine Aquarium Society (CMAS) board that are more then happy to give it away! , those guys are awesome and have helped me out a lot
you don't need much just a few cups and it will be more then enough to seed a sand bed
i just got rid of over 400 pounds of live sand and gave it away! i got it for free from members on CMAS but my tank wasn't going to be ready in time so before i let it die i gave it away.