If you have a basement with a concrete or block wall or anywhere else for that matter give these a try. Weighted sand baseballs. Ron Wolforth has a program that uses these and my son's college program has all of their pitchers do a custom program with these in the off season. I have it on paper but it would do you no good as there is a lot of technique involved in it. You contact Oates and see if they have something or Wolforth.
Good luck.