How can I obtain the deed for a house that

Others will have more experience than me but perhaps the Italian land registry site catastoinrete.it might be useful. My own experience was going to the local land office and getting a copy of what is registered so useful if you have a local friend or relative.

Deeds/acts of sale are held by the notary who did the sale (if he is still in business) or at the notarile archive - if you know the notary and the year he did it, or ultimately at the Conservatoria Dei Beni Immobili in the province/region.     You can find out when your Dad bought by getting a visure catastale storica for the property, or searching under your Dad's codice fiscale for what he owns in such and such an area.   

Please note that the process may vary depending on the specific region in Italy where the property is located. It's also recommended to contact the Italian embassy or consulate in your country for any specific guidelines or requirements.