The two VC-25As and the four E-4s are the only 747-200s left flying, at least in the western hemisphere. The 747-8s the Air Force is buying are being converted and will be officially designated as VC-25B. The original plan was for the last two or three 747-8Is built to be custom equipped and have Secret Service agents observing the entire assembly process at Boeing from the beginning.
During his first term, President Trump decided they were too expensive and directed the Air Force to find a better alternative. The Boeing order was cancelled, and they bought a couple of 747-8s that had been parked because the operating costs. The work to install the needed equipment has been slow and complicated and will likely cost close the to amount the Air Force would have spent for new aircraft.