They’re easy to make.
What I did was make a copy of the fighter torpedo file. I made the weapon be extremely short range, like a max range of 100. I then made the missiles move slowly, but have near perfect accuracy. So they’d move very slowly, such that frigates on keep moving can probably just outrun them, but are very agile. They have a long reload time as well. Their weight is also relatively light such that you can put them on a fighter without slowing down the fighter too much that it become target practice.
End result is what I like to think of as a magnetic mine. Its a chunk of explosives designed to be magnetically attracted to the largest object in the area. Which would be the cruiser you’re trying to bomb. The mine will seek out the hull, contact the hull, and go boom. The extremely short range means that any fighter trying to use them has to fly over the cruiser while dropping the bombs.
A fighter bomber with 1 laser gun and 1 bomb bay is quite effective and flexible. A true bomber with 2 or even 3 bomb bays is devastating against big, slow moving targets like cruisers, but frigates will probably just outrun the bombs.