Sculptamold is basically a finer form of powdered spackle. That can be found at any chain store and used in place of Sculptamold. Sculptamode is widely available at any crafts type store though so it really shouldn't be a problem to find it.
Are you saying you want to use Sculptamold for the surface of an intermodal yard? That I wouldn't recommend. It's pretty expensive for a large yard, messy to work with, and not easy to get looking like smooth concrete. I'd use sheet styrene for the yard surface. A good source of cheap styrene that's just about the right thickness is those "For Sale" signs you can get at Wallyworld.