Outstanding point. People demand to see evidence of the Christian faith outside the Bible. But that just shows their ignorance of the origins of the Bible. Nobody ever sat down to write a Bible and the worshippers of G-d and of His Son, Yeshua, never thought about a book called a Bible. They shared writings from eyewitnesses to help keep their facts straight.
In the fourth century The Holy Church decided that it would be a good idea to collect these documents and bless them so that the documents would be preserved for all time. So they collected whatever they could find that they could be sure were historically accurate and called that the Bible. (The Old Testament was taken rather wholesale from Judaism since the Church accepted the scholarship of the Rabbis on that subject.)
Therefore, if there were another historical document available to the church at that time that bore witness to Jesus it would have been in the Bible. The Church had the greatest libraries in the world. It is unlikely you anyone will ever find anything that The Church didn't know about at that time. If they didn't have it, we're not going to dig it up somewhere.
Now, what the unbelievers would really like is an eyewitness account of everything that Jesus did, but where the eyewitness did not become a Christian.
But I ask, is that reasonable? Could you watch Jesus feed 5000 people with 7 loaves and 2 fishes, watch him heal the blind, the sick, the lame, watch him raise Lazarus from the dead, and finally rise Himself, just as He prdicted - could anyone watch all that and not be a believer?
All the criticism of the historicity of the Gospels is only wishful thinking. John explained it all in John 3:16-21.
Shalom.
Bump. You are right.