Re the USA Civilian use...
In the mid-1960s the U.S. Department of the Interior bailed 3 military Grumman HU-16's from the U.S. Navy and established the Trust Territory Airlines in the Pacific to serve the islands of Micronesia. Pan American World Airways and finally Continental Airlines' Air Micronesia operated the Albatrosses serving Yap, Palau, Chuuk (Truk) and Pohnpei from Guam until 1970, when adequate island runways were built, allowing land operations.
In 1970, Conroy Aircraft marketed a remanufactured HU-16A with Rolls-Royce Dart turboprop engines as the Conroy Turbo Albatross, but only one prototype (registration N16CA) was ever built.
Many surplus Albatrosses were sold to civilian operators, mostly to private owners. These aircraft are operated under either Experimental - Exhibition or Restricted category and cannot be used for commercial operations, except under very limited conditions.
In the early 1980s Chalk's International Airlines owned by Merv Griffin's Resorts International had 13 Albatrosses converted to Standard category as G-111s. This made them eligible to be used in scheduled airline operations. These aircraft had extensive modification from the standard military configuration, including rebuilt wings with titanium wing spar caps, additional doors and modifications to existing doors and hatches, stainless steel engine oil tanks, dual engine fire extinguishing systems on each engine and propeller auto feather systems installed. The G-111s were only operated for a few years and then put in storage in Arizona. Most are still parked there, but some have been returned to regular flight operations with private operators.
Sounds very expensive to get them certified....