One of the biggest affirmations of the existence of the 36 Men of God is that there is a reference to these individuals in two separate tractates of the Talmud. The story seems to be something that was well-known and documented by our sages. We have already seen the text in Sanhedrin. Here, in a similar yet slightly different account it appears in the tractate of Sukkah (45b). The text reads:
Hezekiah further stated in the name of R. Jeremiah who said it in the name of R. Simeon b. Yochai, I am able to exempt the whole world from judgment from the day that I was born until now, and were Eliezer, my son, to be with me [we could exempt it] from the day of the creation of the world to the present time, and were Jotham the son of Uzziah with us, [we could exempt it] from the creation of the world to its final end. Hezekiah further stated in the name of R. Jeremiah who said it in the name of R. Simeon b. Yohai, I have seen the sons of heaven and they are but few. If there be a thousand, I and my son are among them; if a hundred, I and my son are among them; and if only two, they are I and my son. Are they then so few? Did not Raba in fact state [in Sanhedrin 97b], The row [of righteous men immediately] before the Holy One, blessed be He, consists of eighteen thousand, for it is said, It shall be eighteen thousand round about? — This is no difficulty: The former number refers to those who see Him ‘through a clear screen, the latter to those who see Him through a dim one. But are those who see Him through a clear screen so few? Did not Abaye in fact state, The world never has less than thirty-six righteous men who are vouchsafed a sight of the Shechinah every day, for it is said, Happy are they that wait ‘lo’ [for Him] and the numerical value of lo is thirty-six? — There is no difficulty: The latter number  refers to those who may enter [the Presence] with permission, the former [Two – R. Simeon b. Yohai and his son] to those who may enter without permission.
R. Simeon bar Yochai words existed through the generations and preserved in both tractates of the Talmud. He, as noted by Rabbi Dr. I Epstein, was “the reputed author of the Zohar, [and] spent thirteen years in a cave with his son, hiding from the Romans, and suffering great privation.” How is it that a man that was so deprived of life and happiness was able to conjure up the stories of the Lamed Vavnickim? The preservation of the stories, his authorship of the Zohar and the generations preserving the story post R. Simeon bar Yochai has led me to believe that he was at least a witness to the 36 or was himself a Lamed Vavnick. The text in Sukkah suggests that R. Simeon bar Yochai and his son were able to enter into the Presence of the Shechinah without permission, a characteristic of those who are righteous.
As for R. Simeon bar Yochai’s son, who R. Jeremiah and Hezekiah would have known as well, he could have followed his father as a Lamed Vavnick or simultaneously been one of the 36. After all, R. Simeon bar Yochai claims to have seen the “sons of heaven” who Rabbi Dr. I Epstein notes were “those who will see the Presence of God in the Hereafter” noting a potential ability of R. Simeon bar Yochai to know that his son was among the 36 even if not during his own lifetime.