Go out at night when it is raining and use a low power headlamp and look in the yard. If you don't use lawn chemicals you should be able to pick them up by the hundreds. If not, go to the city park or cemetery and see. They are very light sensitive. Over the years l have picked up thousands doing this.
As stated above, if they (night crawlers) are there you will find them on a rainy night on top of the ground. I found a red filter on the light that I used for predator calling to work well for seeing but not spooking them. They can be found in a few locations in the county I live in but are not common, I have tried several times to transplant them to my farm with no success. Good Luck