Hi - first try to trace what happened to that bank (use google to see if another bank acquired it.) or reply in this forum and I can try to trace it.
Next would be to contact that bank - but it may be that the account went dormant and was escheated to the state (assuming you are in the US) . If so then you go to that state's dormant property website and look under your father's name. If you tell me the state I can see if I can find the website
You can use to seek out forgotten accounts on websites like mylostaccount.org. Itcombines tracing schemes set up by the BBA (British Bankers' Association), the BSA (Building Societies Association) and NS&I (National Savings & Investments). You can perform a search using any details you have to hand.