Wouldn't they also be using the UHF (300–420 MHz) band instead of the 'civil' VHF (118–137 MHz)? I know my Bearcat for the KSAT feed skips over some UHF ranges
We are talking about civil aircraft being intercepted by military aircraft. They need to talk to the civil aircraft on a fequency for which it is equipped! If an F-16 comes up along side a civilan aircraft, the default frequency for them to meet on would be "'guard' frequency", 121.5.
Of course that might not be the only frequency they use because the ATC might have facilitated a meeting with the two on another freq. Or they may NEVER actually talk directly. An interception and diversion can happen with no radio communication at all. But I would guess that that is rare.