No, don't buy it. Collect it from very old composted (fully or nearly fully decomposed) leaf piles, create it, or purchase food/bedding especially intended for earthworms/night crawlers. Purchased compost has been sterilized. That's not what earthworms need. They need the live organisms in the dirt/compost. And this reminds me, all this talk of feeding worms oatmeal, organic fruit/veggy pieces, coffee, etc. is all wrong. If we were talking about red wigglers or other composting worms, that would be fine but earthworms do not create compost from these scraps. Putting things like that in with them only invites bacteria and mold, and will likely do nothing but kill earthworms and that's probably why Chantel is having problems with dead worms.

They eat material that is already composted and fully broken down by compost worms, bacteria, mold, etc.. They eat rich earth and that is why they call them earthworms. They don't actually do any composting, and don't tolerate rotting things in their food/containers. If you want to create compost for feeding it to earthworms, then go ahead a create a compost pile and put all those things in there along with plenty of leaf litter, but let compost worms and bacteria do all the work. The rich, dark, musty smelling dirt that this stuff becomes after it has been fully broken down by time and other organisms, is what earthworms/night crawlers eat.