Check with R.W. Norton Art Gallery in Shreveport, LA. They have a lot of pricey guns on display, many are one of a kind. It is possible someone loaned them to their gun display.
I am sure there is a list, a will or something saying where those guns are, if they ever existed, among his paperwork. When I loan a gun to someone for whatever reason, I write down the serial number, they gun type and to whom I loaned it.
A client came in about ten yrs ago and I was hired to find her husband's classic cars that was on loan to an antique car museum. It was learned later that they were not loaned but rather sold to support his gambling habits. I hope this is not what happened in your case.