If @Tath99 had not specified AT, power sets, and blue side preference there would be more room for suggestions.
Elite is what this duo is looking for based on criteria:
Prior to Issue 21, most heroes of natural origin would begin their adventures in Paragon City by contacting ELITE, an organization that specializes in working with heroes of natural origin. Heroes of natural origin will have either Susan Davies in Atlas Park or Derek Amberson in Galaxy City as their initial contact, depending on which zone he or she selects as his or her beginning zone.
If they hadn't been specific, my go to suggestion for natural origin:
Soldier of Arachnos and red side for more concentrated content.
'Natural' covers a wide swath of the game and obviously overlaps greatly. Example: Peacebringers are 'natural'.
@Grouchybeast that looks like great info on enemy groups that could drop the requested SOs.
Natural
Drop Natural SOs and Natural/Technology DOs
Arachnos, Cage Consortium Guards, Dockworkers, Family, Hellions, Knives of Artemis, Longbow, Luddites, Mooks, Paragon Police, Praetorians (Chimera, Tyrant), Prisoners, Rogue Island Police, Scrapyarders, Security Guards, Skulls, Warriors, Wyvern
Player's origin
Drop enhancements that match the recipient's origin
5th Column, Axis America, Council Empire, Hearts of Darkness, Neo-Shivans, Pandora's Might, Rogue Paragon Police, Rulu-Shin, Shadow Shard Reflections, Shining Stars, Turrets, Vanguard Shield, Vanguard Sword, all arch-villains, all Praetorian zone enemies (except "Praetorians")