if you can wander around various places you can flip up a rock or piece of wood and likely find worms under it or in it. especially if it is damp. you should not have to buy worms.
the problem if you have chickens is that they are going to scratch and get rid of a lot of your worms if you don't have deep enough litter and enough protected places for them to hide from predation.
you can buy red wrigglers and other composting worms to put in your gardens but they will wander around and get eaten by the chickens too if given a chance to get out. so i keep worm buckets inside so that the birds and other predators cannot reduce the population until after i use them to fertilize the gardens. after that they are on their own (and a few do survive but it is only a fraction of a percent of what gets put into the garden).
i don't go out of my way to pick up the worms but they don't hurt or bite. i have large metal spoons (that you often see in food service trays) that i use to dig in the worm buckets when i need to add stuff to them. it's too hard on my hands to dig in them most of the time as it is also often too hard to dig in a garden with my hands (we have mostly clay subsoil) so i have my shovel, trowel, knife, hoe, cultivator, etc...
