Adding onto it again lol, Czech Airlines A330-300. It was leased from Korean Air for flights mainly to Seoul between 2013 and 2020 as per below, so a regular part of the fleet and the Prague landscape for 7 years. This was due to Korean Air owning a majority chunk in the airline until 2017 when it sold it to Smartwings.
Now you might say ‘Well there was only the one so what’s the issue’, ah my good friend I will reveal it, the B738 we have as a regular livery in-game for Czech Airlines was itself merely a one-off, being transferred from new parent Smartwings.
The A333 would make for an excellent addition to Prague and open up many long haul destinations, providing players the option of what sort of airport they wish to run.
Another is the relatively recent addition of the American Eagle E140, a livery worn by all 68 of American Eagle’s E140s
Some wore it into 2018 with Envoy Air,
Another potential candidate would be Austrian’s CRJ-200’s of which Austrian Arrows operated 13. These were all retired in April 2010 so cutting it a little fine, however, they could make for an excellent addition to new players at INN and were seen operating on routes across Europe during their heyday.
Another is a second relatively recent addition, that being Malev’s Fokker 70. Malev was the Hungarian flag carrier until their sad demise in 2012, operating a fleet made up of Boeing’s with Q400s and 6 Fokker 70s mixed in. The Fokker 70s were operated by the airline across Europe including to Zurich, conducting its final flight just past the dev’s cutoff point on 16th January 2010 from Tirana to Budapest, the type then being sold on by December that year. It would add the airline in and a snazzy scheme for players to operate into their airports.
A final one off the top of my head, Aerosur. Both their 747-400 and 767-200 are special liveries, being seen around South America with the 747 straying into the North from time to time and SYD. Both were single aircraft in the airlines fleet so there was no main livery per se, as displayed with the 737-300’s and 737-200’s which both flew with the airline until 2012 and both had 5 each in the fleet, all of which wore different liveries. One 767-200 was operated until 2009 before being scrapped, wearing what could be a regular livery, but it wasn’t seen after 2010 so would never be added.