Made a list of where you can find what Neutral upgrade for the current Expansions. Mainly did this to speculate what upgrades for the next expansions are.
Anything marked Core is included in the Essentials
LAB = Latari Army Box
Reaping Blades* [Core]
Fortuna's Dice* [DInfUp, WInfUp, LInfUp]
Shield of Margath* [Hawthorne, Maro, Maegan]
Rank Discipline [Core, DInfUp, Carrion Lancer, LAB]
Flank Guards [