Recently the f-102 and j35 were given weaponry which is compatible and historic with the f-106 while the f-106 remains missing the features.
The f-106 in game is equipped with a gunpod that mounts in the aim26 hardpoints, this gunpod should be removable in game so that the aim26 can be used.
Discussion from the f-106 association Armament M61A1 Cannon | F-106 Delta Dart
video
Historic video of the gun instillation https://www.youtube.com/watch?v=9sD7cOpBgJQ
As noted by other users, the rb28/aim4A would be a significant upgrade over the aim4f/g currently available.