Ebionites. Everything else of the Omnium Gatherum as it existed in the 1800s can be readily found. Not the Ebionites however. Only a bit about them has survived and yet Blavatsky referred to them quite extensively. Which likely means she was telling the truth about being instructed by them or perhaps she made it all up.

If you check Wikipedia on them you'll find a little, not a lot.

A lot of their politics, economy and some etceteras are reflected in Oz.

I'll hit some of the more significant points - as defined by Blavatsky - and if I have to add anything as I go through the books I will.

First of all, who they are or were. They are the followers of Jesus of Nazareth who were located in Jerusalem until the destruction of the Temple. They consisted of Jews and Gentiles and considered Paul of Tarsus to be the False Prophet mentioned in Revelation. The only two books of the "New Testament" that they accept as valid are their versions of Matthew and Revelation. They consider all the rest to be Pauline nonsense and blasphemy. Since they do not consider Jesus to be the Messiah they do not call themselves Christians, as Christ means Messiah. They do not believe in the virgin birth and their version of Matthew which they consider to be the original has nothing in it about virgin births and they consider Jesus to have been born naturally along with his four brothers and two sisters.