There are 2 more ways than what you listed.

GC daily supply and provision mission, you get a new one daily for every DoL and DoH class you have, The are like 1 free leve, that gives xp and seals instead of $. For DoH you hand in 1 item chosen at random for your current level range. For DoL you hand in 10, Fish is 5 or 10 depending if it requires mooching or not. Even at low levels doing them all will get you enough to buy the lesser xp book.

Then once you get your GC rank up to the 2nd rank of 2nd tier, you get expert delivery missions. These just let you trade in any pink or green equips for seals.