Extra-Biblical evidence is not required since scholars agree Gal. 1 & 2 and 1 Cor. 15 are authentic, that Paul really believed what he wrote. Limit yourself to the Minimal Facts Approach of what scholars agree on. That is not to say there is no extra-Biblical evidence like the Talmud, Tacitus and others about Jesus who comment on His miracles, deity and resurrection. Of 45 earliest ancient documents 17 are non-Christian of which 7 of those 17 speak on his resurrection, and 7 speak of His deity. 24 of the 45 speak of His resurrection. 12 of the 17 non-Christian refer to His death. And several refer to miracles of sorts.

The reason extra-Biblical evidence is still unimportant though is because the secular world could care less about the Savior of the world and only refer to Him in passing. To give you an analogy that is like asking a hockey fan to make a comment about the teams in the NFL when he could care less about football. Therefore, we can only cite the multiple eyewitness testimonies at the time when it happened, and if you can not account for their claims, then know it must be true. Modern psychology says there is no such thing as group hallucinations, that is, multiple people seeing something that is not there. It's impossible. So if you can't account for the resurrection of Jesus otherwise, then give your life to Christ.