Generating your own checklist in advance of and in preparation for an internal audit (assuming you are the auditor) can be one of the best methods to actually prepare for the audit. Primarily, it will help you plan the audit and it will refresh you on what the actual requirements (of the standards and your own internal processes) are. It should help you think logically through your processes, their interactions, and the best order to review them, and will help ensure that you hit on all the relevant topics. It should also help you think critically about where the risks (operational, safety, compliance, or otherwise) are.
Maybe some people can get all that just by reviewing something someone else put together, but I personally learn/refresh best by writing things down for myself.
So all that goes to say that even if you do find an off-the-shelf internal audit checklist, I would highly encourage you to generate your own.