There are pure incarnon weapons which are available through Cavalero in the Ten Zero social space.
https://warframe.fandom.com/wiki/Cavalero#Offerings
There are incarnon genesis adapters which can be applied to existing weapons, these are acquired by doing Steel Path Circuit rotations from Duviri
For the original batch of Incarnon weapons, i.e the Phenmor, Laetum, Innodem, Praedos, and Felarx, you can get them all through Cavalero. They're all sold as blueprints, buy 'em, craft 'em, there ya go.
For the Genesis weapons, i.e the newer batch that released with Duviri, they're all given through Steel Path Circuit as part of its weekly rotation. Each week has 5 choices, you can pick 2. These give you adaptors that you install onto its associated weapon. For specifically and only the Week 2 incarnons, i.e Gammacor/Boar/Angstrum/Anku/Gorgon, you can also buy them for 120 plat straight from Cavalero in his usual Zariman Spot. These give you the adaptors and all the resources needed to craft them.
Once you have an incarnon weapon or installed an adaptor onto a pre-existing weapon, you can complete challenges that let you get evolutions to give them added perks. The final ones are usually the most enticing. The Genesis batch, notably, tends to have stat changes that effect the base stats of a weapon, like giving the Ceramic Dagger a beefy crit chance stat....that conveniently also extends to Gara/Atlas/Khora, just as an added little perk.
Thanks for your explanation. I didn’t realise about the Genesis weapons released with Duviri. How viable are the original incarnons for SP?
The five OG Incarnon weapons are craftable via farming in the Zariman missions iirc.
Cavalero sells adapters for plat for a handful more - and the rest are on a weekly rotation from the circuit in Duviri on Steel Path.
So - the first five are regularly crafted, very powerful weapons with multiple fire modes and evolving stats. The rest are adapters addeded to older (mostly obsolete) weapons to turn them into hand held war crimes with multiple fire modes and evolving stats.
If you just started on The Zariman, the OG Incarnon weapons will likely be a great addition to your arsenal - there are two primaries, a secondary and two melee weapons. To unlock their full potential, you'll need to build one of each type.