It is possible to make a gun fire multiple shots at a time. There are unused gun models capeable of firing two and five shots simultaneously.
As for making a spread, I am not certain that would be possible. Freelancer's aiming system tends to point lasers twowards the target when you aim at the crosshair, even if you could get them to fire out on an angle it is likely that each of those shots would still home in on the targer. But I haven't tested it, only a theory.
Simplest way to do it would be to make it an explosive (like a missile) that does not track. However I'm not sure if this would work either, because from experience, firing 5 missiles from a single gun at the same time results in either an instant explosion or the rockets sitting still in space.