Where did that New Testament come from?

Answer: the Old Testament, which as mentioned in the previous post, was preserved by the Jewish people. If we cross out every direct quote and allusion to books of the Old Testament in the New Testament, we wouldn't have much of a New Testament left.

image: Khaburis Manuscript, copy of a 2nd century New Testament (source)

The following findings and quote are from New Testament use of the Old Testament by Roger Nicole

Researchers' findings in New Testament
C. H. Toy lists 613 O.T. references.
Wilhelm Dittmar lists O.T. 1640 reference.
Eugen Huehn indicates 4105 passages in New Testament reminiscent of Old Testament Scripture.

"If we limit ourselves to the specific quotations and direct allusions which form the basis of our previous reckoning, we shall note that 278 different Old Testament verses are cited in the New Testament: 94 from the Pentateuch, 99 from the Prophets, and 85 from the Writings. Out of the 22 books in the Hebrew reckoning of the Canon only six (Judges-Ruth, Song of Solomon, Ecclesiastes, Esther, Ezra-Nehemlah, Chronicles) are not explicitly referred to. The more extensive lists of Dittmar and Huehn show passages reminiscent of all Old Testament books without exception." << source

Table of Old Testament Quotes in the New Testament
The Importance of the Old Testament to New Testament Christians
Old Testament God vs. New Testament God