And this is why everyone should have a list of policies, companies, etc., put in a safe place where the executor of the estate can find it.
Check through all the cancelled checks you can find and see if any were written to an insurance company as a premium payment. Call the Bank and see how far back their checking account records go and if you can see them. Then, get out the yellow pages and start calling the largest companies -- i.e., Aetna, Allstate, State Farm, Jackson National, Sun, etc. (surf the web for more). First ones you should call would be the ones who do the most advertising in your area. I don't know of any central databank for this stuff. It is all going to be leg work.
I do think, however, that after a person dies, if the insurance company receives knowledge of it and doesn't pay out the claim for one reason or another (say, the beneficiary is dead also), then within a certain time period, they must turn over the money to the State as being unclaimed -- in which case, you contact your State's Comptroller's Office for unclaimed funds. However, unless the insurance companies keep track of the obits, or a premium payment is missed and they send notice of cancellation for non-payment to the deceased home, I really don't know how they would know.
If it's a paid-up policy, well then you have to find the policy or get lucky calling the insurance companies.