Reach: Drop sources, locations, and probabilities

Tips

Here are the missions where you can get Reach in Warframe:

Uranus/Rosalind : It's a Spy mission (level 27-29). The item is dropped on rotation C (7.04%).
Neptune/Nereid : It's a Spy mission (level 30-32). The item is dropped on rotation C (7.04%).
Pluto/Oceanum : It's a Spy mission (level 32-36). The item is dropped on rotation C (7.04%).
Sedna/Kelpie : It's a Spy mission (level 35-40). The item is dropped on rotation C (7.04%).
Deimos/Cambire : It's a Alchemy mission (level 55-60). The item is dropped on rotation C (12.00%).

These recommendations are based on the usual missions lengths, and the probability of getting the resource dropped.

Spy: One rotation level gained per vault unlocked.
First vault is rotation A, two vaults is rotation B, all three vaults unlocked is rotation C.

Ennemy	Probability
Profit-Taker	14.1%
Coolant Raknoid	11.62%
Terra Elite Embattor Moa	7.59%
Jackal	7.59%
Terra Anti Moa	7.59%
Terra Elite Raptor Sx	7.59%
Terra Embattor Moa	7.59%
Terra Jackal	7.59%
Terra Railgun Moa	7.59%
Terra Moa	7.59%
Terra Raptor Sx	7.59%
Terra Shockwave Moa	7.59%
Terra Ambulas	7.59%
Hellion Power Carrier	6.32%
Scyto Raknoid	3.79%
Aurax Atloc Raknoid	3.79%
Narmer Scyto Raknoid	3.79%
Narmer Raknoid	3.79%
Narmer Mite	3.79%
Mite Raknoid	3.79%
Kyta Raknoid	3.79%
Raptor Rv	1.9%
Raptor Mt	1.9%
Raptor Ns	1.9%
Raptor	1.9%
Eidolon Vomvalyst	1.26%
Deimos Mutalist Osprey Carrier	0.76%
Nightwatch Carrier	0.76%
Deimos Runner	0.76%
Corrupted Power Carrier	0.76%
Corpus Power Carrier	0.76%
Axio Crewman	0.76%
Vapos Crewman	0.76%
Volatile Runner	0.76%
Narmer Power Carrier	0.76%
Grineer Power Carrier	0.76%
Mutalist Osprey Carrier	0.76%
Orm Crewman	0.76%
Orphid Husks	0.76%
Narmer Crewman	0.76%
Kuva Power Carrier	0.76%
Taro Crewman	0.76%
Kuva Hellion Carrier	0.76%
Crewman	0.76%
Vorac Crewman	0.76%

Other items:
Breach Loader - Necramech Reach - Augur Reach
Auto Breach - Primed Reach - Sinister Reach