Mikoyan-Gurevich MiG-19, Bulgarian users

The MiG-19 was the first Soviet supersonic fighter and it was exported to many foreign countries.
The first country it was exported to was Bulgaria. During late 1957 and early 1958 the Bulgarian People's Army Air Force (BPAAF) received 24 MiG-19S fighters, with the first 12 of them being assigned to the 19.IAP (Fighter Regiment) based at Graf Ignatiev Air Base, close to the city of Plovdiv.
A total of 59 MiG-19S and MiG-19P served with the BPAAF on four squadrons. The 11.IAP based at Gabrovnitsa Air Base, the 19. IAP, and the 10. IAD/21. IAP based at Uzundzhovo Air Base between 1959 and 1970. In some sources the retirement date of the last MiG-19 is set in 1978 as some MiG-19S were reconverted to the ground attack role by replacing their drop tanks with two FAB-250 bombs.
When the 11. IAP was disbanded in 1960 its MiG-19S and MiG-19Ps were transferred to the 18. IAP/ 1. IAE (fighter flight) based at Dobrostlavtsi Air Base, near the capital, Sofia. Additional second hand MiG-19Ps were acquired from Poland in 1966.
Some reports claim that there were also 12 MiG-19PM serving with the BPAAF, which were also acquired from Poland. That would make Bulgaria the first Warsaw Pact country to use the MiG-19 but also the last one to use the missile-equipped MiG-19PM.
In 1969 the MiG-19Ps that were still in service with the 18.IAP/1.IAE were upgraded with two APU-13 launch rails for K-13A missiles, making them the most heavily armed aircraft of the BPAAF with two NR-30, two ORO-57K FFAR pods and two K-13A air-to-air missiles. Those aircraft, known in some sources as MiG-19PT, served until 1975 and were sold, dismantled, to China.
Bulgarian People's Army Air Force's elite unit, 1.IAE of the 19.IAP often made practice interceptions against Soviet Tupolev Tu-95 and Tupolev Tu-16 bombers flying in high altitude training missions.
Given the complexity of the conversion training and maintenance difficulty of the MiG-19, some units retained their MiG-17F, which had still in the 1960s a good reputation of being a fast and agile dogfighter. The MiG-17F was used mostly for low-level combat and battlefield air defence, while the MiG-19s were tasked with all-weather interception of high-flying targets, namely, NATO nuclear bombers which would have to traverse both Bulgarian and Romanian airspace on their way to targets in the USSR.
The MiG-19 wasn't very liked in the BPAAF as it suffered from poor engine reliability. In fact, of the 58 total aircraft supplied, 28 were lost in crashes, killing 15 pilots, making an attrition rate of 48.2%, similar to the Lockheed F-104 Starfighter one, or, in another words, one accident per 1.000 flight hours. In fact, low serviceability and high attrition rate forced the 21.IAP to replace their MiG-19 with the MiG-17F/PF.
Some other sources claim, however, that only one pilot belonging to the 18.IAP/1.IAE was killed when he flew his aircraft into the ground due to de-orientation in clouds and that most non-fatal accidents with the MiG-19 were caused by poor maintenance.

Sources:

1. https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-19#Variants

2. Midland Publishing - Mikoyan-Gurevich MiG-19. The Soviet Union's First Production Supersonic Fighter

3. Salamander Books - The Complete Book of Fighters