Megan,

KMR is the best milk supplement. Also get feeding bottles. They should be right near the KMR. You'll need to put a hole in with nipple with a sewing needle to make sure the milk comes out. The powdered stuff is the best and goes a long way.

I really think you need to get this kitten to a vet ASAP. The mother is rejecting it for a reason. Usually they have a second sense about the well-being of the kitten. It could be the kitten has something wrong with it.

Kittens that small need to be fed every 2-3 hours. They also will need help in eliminating, i.e., peeing and pooping. You can do that with a cotton ball. After feeding, gently rub a cotton ball on it's bottom. If you've ever noticed a mama cat licking her babie's bottoms, that's the same principle.

When you bottle feed him, make sure he's in the same position he'd be in if nursing from the mama (on his belly). This way he won't aspirate any formula into his lungs. Hold his head between your fingers of one hand. Please, if you can, get him to the vet.