Guard reps have always been easy to get, with the exception of the Zoner Guard. For everyone with missions - you simply grind them (20 or so + a bribe will give full guard rep).
Guard tags on the other hand, are practically useless, and only show you've spent more time repfixing your character.
You do not need a guard tag to get a capital ship / buy stuff from a Guard system. You only need full guard rep.