I'm looking for a rock that i can carve for a waterfall on my mom's koi pond?
Find a stone supplier near you. They will have to drill a hole in it so that water can come up through it. Carving a rock is probably not possible for you unless you have specialized equipment. You could check on lava rock. If you find a lava rock boulder, you will be able to work with it, but be sure you wear heavy gloves because it's sharp.
To find more pond information, go to pondlady.com