At one time or another virtually every Colt model was bought in at least some quantity by the US government for various agencies and departments.
The US Post Office bought:
The Colt Detective Special.
The Banker's Special.
The Colt Model 1917 as surplus from the Army.
The FBI bought:
The Official Police.
The Government Model .45 for special use at various times.
The Government Model Super .38 for special use.
The Python was an "in" gun with FBI as a personal gun.
The US Border Patrol bought:
The Colt New Service.
The Border Patrol model of the Official Police.
The Border Patrol model of the Trooper Mark III.
Other Government purchases were the Trooper, the Trooper Mark III, the Detective Special, the Cobra, the Agent. etc.
Numbers are mostly unknown except for the Border Patrol models.