You can get the rest of the souls, one at a time, from doing quests in Meridian/Sanctum starting at level 13.
But, as someone who's main IS a Riftblade/Paladin/Reaver, those three are definitely very solid soloing souls and together they can make you pretty hard to stop.
This is my current build at level 46: http://rift.zam.com/en/stc.html?t=0cALh.Vuoxz.vMotds0Gtzz.xb
the next point goes into Small Arms Specialization and will give me the 10 minute full heal from Paladin. I run with a one-handed weapon and a shield (also scissors but that's a different issue) and I can solo most anything that can be kited. Also, crit and dex are the only stats that matter to a Riftblade, str is pretty meaningless, though you'll get some from your gear anyway.