Go to the county probate court for the county in which your grandfather lived. Ask them to see the file on his probate. The will and all accounts that executors are required to submit should be in that file. If you believe you have been wronged, you have the right to file an objection.
Do you know for certain that your grandfather had a will? If he instead opted for a trust, then you will need to directly communicate with your father, demanding a copy of the trust.
This answer is provided for informational purposes only. Actual legal advice can only be provided in an office consultation by an attorney licensed in your jurisdiction, with experience in the area of law in which your concern lies.