If you don't have dry beans or forget to soak them, canned beans could be substituted. I'm guessing you would need about 4 cups, but use as many as you like to make the soup the consistency you want. I suggest rinsing and draining the canned beans before adding them to the soup. The soup will not need to be cooked nearly as long because the canned beans are already quite soft. Just cook long enough to cook the onions and mushrooms and meld the flavors together.
Be sure to refrigerate the ham broth *overnight* before taking the fat off. This way you can be sure that all the fat rises to the surface.
Again, if you want to make this soup for supper, you could either just leave the crockpot on "keep warm" all afternoon or adjust the cooking temperatures and time frames according to your schedule. You could soak the beans all night and then assemble the soup in the morning. You may need to set the crockpot to "high" for an hour or two to soften the beans. Add the mushrooms a few hours before serving and continue to cook on low until suppertime.