A significant number of Narmer Isoplasts are needed to build the four weapons and the Warframe that require them—and even more if you plan on making a second of the Warframe to subsume with the Helminth.
Where to get Narmer Isoplasts
Narmer Isoplasts can be obtained from Narmer Bounties.
Narmer Bounties can be found on Cetus while Cetus is in its day cycle and on Fortuna while Cetus is in its night cycle.
The Narmer Bounties have three different rotations, but the likelihood of getting Isoplasts is the same no matter which rotation you participate in.
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Farming for them
We recommend that you farm for them on Cetus when possible. Bounties on Cetus are faster than Fortuna bounties in our experience. We have also experienced fewer run-breaking glitches on the Plains of Eidolon than in the Orb Vallis.
Yout can also expedite one of the worst objectives that are often in Cetus bounties. The drone escort objective is ordinarily a massive time-sink, but both Loki and Nova can make it one of the fastest possible objectives by teleporting the drone. The same applies to the rescue objective, though that one is fast either way.
If Loki or Nova aren’t available to you, then any Frame with high mobility or AOE for any exterminate objectives is a good choice. Having enemy radar is also a great idea.
You’ll need 94 Narmer Isoplasts for everything that builds from them, or 134 if you plan on making a second Caliban to subsume.
For information on how to get Caliban, go check out How to get Caliban in Warframe on Pro Game Guides!