The list above was good, but with recent updates, it got changed. There are more Warframes and new locations.
Boss Drops - Each one must be killed 3+ times to get each part.
---Rhino - Jackal (Fossa(Venus))
---Oberon - Vay Hek (Everest(Earth))
---Valkyr - Alad V. (Themisto(Jupiter))
---Mag - Nef Anyo (War(Mars))
---Ember - Sargus Ruk (Tethys(Saturn))
---Trinity - Lech Kril + Vor (Iliad(Phobos))
---Ash - Tyl Regor (Titania(Uranus))
---Loki - Hyena Pack (Psamathe(Neptune))
---Frost - Lech Kril (Exta(Ceres))
---Excalibur - Ambulas (Hades(Pluto))
Research Drops - These must be researched in the clan dojo.
---Zephyr - Tenno Research
---Banshee - Tenno Research
---Volt - Tenno Research
Prime Drops - These are earned from the Orikoin Void and Derelict Missions. The locations sometimes change, so I would advise looking at the Wiki to double check the locations.
(http://warframe.wikia.com/wiki/Orokin_Void , http://warframe.wikia.com/wiki/Orokin_Derelict)
Random Boss - The only random boss Warframe is Nyx, who drops from Phorid manifestation. A Phorid manifestation appears when an Infestation outbreak reaches a boss fight.
Alert - The only alert warframe is Vauabon. He is extremely hard to get seeing that there is a very low chance that when an alert appears, it will be a part. And, if it is, there is always the chance of it being one you already have.
Quest - Purchase and build the quest from the market and complete it to get parts of Mirage and Limbo.