Even though the B-17 was ineligible for a FAA license to carry revenue-paying passengers, several were converted as business or executive transports and used for a while by American corporations. These conversions were essentially similar to the wartime CB-17/XC-108 cargo transport conversions. A few surplus B-17s were even converted into cargo transports with XC-108A-type cargo doors installed.
Several ex-military B-17s were fitted with extra tanks and were used for spraying operations.
In 1960, the first of 23 ex-military B-17Fs and Gs were converted into fire-fighting aircraft. The bomb bay was reconfigured to accept a 2000-gallon tank which carried a water-borate mixture to be dropped on forest fires. The tank was divided into four compartments, each with a quick-opening bottom which allowed the water to be dropped. These planes were operated under contract to the US Forest Service, and a few were still flying as late as 1984.
By the early 1980s, most B-17 water bombers had been grounded, mainly due to the lack of Wright R-1820 Cyclone engines. One water-bomber operator solved this problem by installing Rolls-Royce Dart turboprop engines in place of the Cyclones. This was done for B-17G Air Tanker N134ON. N1340N crashed in October of 1970, when fire smoke caused engine failure in the Dart turboprops.
The Institut Geographique National of France operated thirteen B-17s during the post-war years to perform worldwide survey and geophysical research missions.
USAAF Serial French civil Disposition 42-30177 F-GBSG used for spares, scrapped 1973 42-32076 F-BGSH currently on display at WPAFB Museum 43-39304 F-BDAT Destroyed in 1950. 44-8846 F-BGSP Still flying in France 44-8889 F-BGSO on display at Musee de l'Air 44-83728 F-BGOE scrapped in 1970. 44-83729 F-BEED scrapped in 1962. 44-83735 F-BDRS with Imperial War Museum. 44-83757 F-BDRR scrapped 44-85594 F-BGSO scrapped in 1972. 44-85643 F-BEEA destroyed in 1989. 44-85718 F-BEEC with Lone Star Flight Museum 44-85733 F-BEEB destroyed 1949. 44-85784 F-BGSR with B-17 Preservation Ltd.
In 1999, there were 43 B-17s that still survive. Only about fourteen of them are flyable or capable of being made so. Another twenty-three are on static display in various museums. Four B-17s are currently undergoing some sort of restoration. Four are abandoned hulks that consist of little more than bits and pieces of aircraft that are being held in reserve to support future restorations. Two are in storage at the National Air and Space Museum.
Another 17 B-17 airframes are believed to be in known locations at crash sites throughout the world, and may be recovered in the future.
Today, the only B-17s still flying are those that are used by such organizations as the Experimental Aircraft Association, the Collings Foundation, and the Confederate Air Force as "flying museums".
A list of surviving B-17s can be found at the Aero Vintage Books website, which can be accessed by clicking here. It draws heavily from the book Final Cut by Scott Thompson. You might want to check this site for frequent updates. Also listed there is a table of all B-17s that have had civil registrations over the years.