Where can I find information on obtaining Soul Crystals to upgrade my warrior class?
For clarification, you're not a Warrior until you have the Warrior Soul Crystal, you're a Marauder until then.

I would have kicked them too at level 50, Marauder is not viable as an end game tank due to missing so many integral skills needed to tank, mainly Defiance. I don't know how someone could miss the quest that directs you to your advanced job when the bread crumb quest giver is right next to the guild.