Nothing else besides what we see in the NT and other early writings, if that's what you mean. To spell it out a little more, I'm thinking that in Capernaum where he lived, and among the many other disciples besides the twelve, and in the crowds that came to hear him, there would have been people taking notes and writing letters and teaching aids, just like in any other teaching network. Those would have survived long enough to be the Q, L, M and other sources that scholars are imagining. If you have some reasons for thinking that didn't happen, I'm interested.
Let's live his life for a minute.
He is from the tribe of Benjamin and a pharisee when is about belief.
He, as assumed, assisted to the Temple or a synagogue on Sabbath.
The "service" was the reading of portions of the scriptures. No preaching.
Suddenly, the synagogue started to be visited by lots of gentiles. And the number of them was increasing each following week.
This increase of new visitors to the synagogues was caused because the advise of the Apostles. It happened that Jews who became followers of Jesus teaching started to tell the gentiles that they must get circumcised because otherwise they won't be considered to be inside the promises. Discrepancies increased because the argument made about circumcision and both sides went to the apostles to hear what they have to say about it.
The apostles weren't the new priests, their mission wasn't to read the Torah portion every Sabbath, they were told to announce the good news, that's all. Just look Peter trying to read the Torah when he was just an illiterate fisherman.
So, after having a meeting, they came out with a sure solution: to tell them to abstain of idolatry and other rules, but for the new converters to visit the synagogues on Sabbath to listen and learn the Law. (The bible says " listen Moses" but implies the Law).
And the converted gentiles started visiting the synagogues to learn the origin of that religion, the books of Genesis and more, because there weren't available libraries, books and similar to learn the Torah but going to the specified centers of meeting.
Then, synagogues started to be full of converted Jews and gentiles who were interchanging their views and learning about the scriptures and what Jesus said, the good news.
Lots of Jews weren't happy to see those new converters to the good news inside their synagogues.
Here is when Saul decided to make the first Crusade registered in history. He wanted synagogues to be free of new converters. The priests gave green light to persecute and kill those new converted, specially the Jews ones. For them a clean up was necessary.
But this was not pure fanaticism.
Saul had to learn what the new converters believed. In other words, Saul learned a lot about the new religious tendency that -according to him- infiltrated inside the synagogues. This is very common, to know well the enemy.
Then, Saul wasn't persecuting converted Jews and gentiles in the streets but in synagogues.
This is the Saul before his conversion.
By the way, this is my point of view, if you read the same educated guess scenario from above in another place, it must be a copy of this point of view written by me here but some decades ago online.