While the game might be "solo-friendly", it doesn't mean that you will be able to solo everything. Jobs are meant to be played in a party, and as such some quests require a party to complete. Classes are meant for soloing, and you don't need to do anything to unlock those other than purchase a starter weapon.

Suffice it to say, if you want to unlock a job tailored for party play, you will have to party with other people to do so. Can't hurt to find a nice linkshell and start making some friends. Friends help each other out, it's just what they do. I'm sure people won't have an issue with helping you with your job quests. They can scratch your back, you can scratch theirs.