Carob Trees grow all over North America. I was able to forage a shopping bag full for free from the streets in Los Angeles and process about 3 pounds of powder in one weekend. The stuff is fairly easy to process at home, with the proper equipment. It helps to have a dehydrator and a VitaMix or some other kind of high powered blender, but a regular blender and a low temp oven might just do as well.
Step 1: Wash and boil
Clean your pods. They have probably been out in the world collecting all kinds of lovely smog and dust. I scrubbed 'em with some veggie wash. Carob is subject to mold and critters, but the ones I collected seemed pretty clean. I only picked the pods still on the trees, and only if they looked healthy and shiny.
The pods are kind of hard, and you want to get the seeds out, so unless you are fanatical about keeping your carob raw, boil them for about 20 minutes.