I have replaced them with regular boat winch. Just make sure you get one rated for enough weight for the cattle you plan to put on it. If you are only going to do steer you should be able to get by with a 2000 lb. winch.
I use a table that our ag teacher put a battery operated athletic winch on. Saves on cranking but you have to keep the battery charged. It has a remote which is handy when you lay them down if you are short handed.
You can buy winches at most farm supply or automotive stores. I would look for one rated at 3000 lbs or more because they should be heavier built.