There isn't a game setting for that, in MekHQ or MegaMek. The closest I can think of would be to back out the EnemyAirSupportBombers scenario modifier from the groundBattleModifiers manifest file which will prevent dedicated bomber formations showing up. You might also look into modifying the scenario template and modifier XML files, which have an allowAeroBombs element that can be set to 'false'. Otherwise you need to walk through them manually, which I also do if just to tone it down or select something more appropriate e.g. a full bomb load on a heavy fighter typically leaves them with an impractical thrust value, or F-rated pirates get air-launched Arrow IVs replaced with rocket launchers.
Best bet for dealing with pesky bombers is to deploy your own fighters on overwatch. If you're not willing to spend the support point to deploy reinforcements, you can always add them as 'free' via manual deployment from the TO&E. Tactics can also assist keeping your units alive - keep them to the corners where fighters have a hard time making the turn while staying on the map to make an attack. Identify locations where fighters cannot get to and move into those dead zones, preferably close to the starting point of the flight path where you can take potshots at them (if they stay on the map).
