You want red wigglers worms. You can probably find a dozen anywhere you can find fishing bait. They are skinnier than earthworms and they have distinct stripes.

Drill lots of holes in a 5 gallon bucket and bury it next to the compost pile. Fill it with used coffee grounds, kitchen scraps, blended egg shells and every banana peel you can get your hands on. I tear up the cardboard egg cartons and throw them in, as well.

The worms will breed out of control and will completely populate your compost.

Since you have a backup supply in the bucket, you never need to worry about harming the ones in your compost. The worms will live through all weather (as long as they can stay moist). Even if it sits at -15F for 8 weeks, some eggs will always survive.

They aren't supposed to like temps under 40F but the Chicago outdoors hasn't been able to kill mine in 5 years. All my raised beds are populated with them and even the dying tree had worms 4 feet up the trunk where it had a spot that was rotting.