I'm trying to locate a manufacturer currently making a 12 gauge
shotgun choke available to the public that spreads, or disperses, shot
horizontally. At times these were referred to as "duckbill" chokes,
since they resembled a duck's bill. Alternatively, information on a
retail outlet that carries these would also be accepted as answer.
Thanks.

I saw your question the last time you asked. I have tried very hard to
find a supplier. I believe that there may be persons manufacturing
these chokes, but they are afraid to admit it. This is very likely a
product reserved strictly for police/government use.