Unfortunately there is no easy solution to your case. The only central database that would enable you to find out who he applied for coverage with--MIB (Medical Information Bureau) keeps track of all applications for life insurance policies including name of company and amount applied for.
MIB has a policy locator service and maintains the records going back fourteen (14) years. Their website is http://www.mibsolutions.com/lost-life-insurance/.
If that does not work, i.e. if your dad purchased the policy over 15 years ago, you will then have to do a manual type search. As far as I know if you are the Executor of the Estate you can access bank records to see who he paid. The other alternative is that he might have had a safety deposit box at the bank that you might not be aware of. If you are the Executor you should be able to 1) find out if he had a box and 2) if he did the bank will let you open it.
I can also suggest that you check with the HR Department at his job since he might have made you a beneficiary on his life policy at work. If not also check with his auto and homeowners agent--he or she might be the same person who wrote the life insurance or might have referred him to the person. Also if he had an accountant or the family attorney try checking with them since he might have given them the information while writing his will or checking tax implications of the life policy. Also the attorney might be able to come up with another way to check assets. Did your father fill out a Net Worth Statement for anything recently--the information would be listed there.
If there are no other options, you are left with calling companies individually. However, be forewarned the last information I had was that there are over 1800 life insurance companies in the U.S. alone and over a 15 year period many of them might have changed names as a result of mergers, etc. If you have to go this route, first go to the insurance commissioner for your state and have them give you a list of the companies licensed in your state, i.e. not all companies are licensed in every state then with the list first think of the top names of insurance companies on the list--the companies that have the most name recognition and start by calling them, i.e. New York Life, Metropolitan Life, Mutual of Omaha, Sun Life, TransAmerica Life, AIG, Prudential, Northwestern Mutual, Pacific Life, etc.
In short this is a daunting task, my bet is that he had a safety deposit box or was covered at work.
I am very sorry for your loss. Good luck!