There are no non-biblical accounts to the resurrection
First of all, saying that there are no non biblical accounts of the resurrection does not invalidate the resurrection. The New Testament documents, particularly the Gospels, were written by eyewitnesses or under the direction of eyewitnesses before the death of the apostles. Therefore there were plenty of people around who could have contested the post crucifixion appearances of Christ. We must first understand that the Gospels are historical documents and they are reliable ones.
Second, it is not accurate to say that there are no extra biblical accounts of the resurrection of Christ. There are other historians who have written about this. However, the problem with most of them is that they were not contemporaries of Jesus. They were written well after the fact. This, therefore, tends to invalidate the reliability of these extra biblical accounts according to the critics. But if the extra biblical accounts are not valid because they were written after the fact by non eyewitnesses, then that indirectly supports the gospel accounts which were written by the eyewitnesses, by those who knew Jesus, and encountered him after his resurrection.
Third, how do you have witnesses to the resurrection? Even the disciples didn't see Him rise from the dead. Instead, they saw Him after He had risen, as was evidenced by the wounds in His hands and side when He appeared to them (John 20:27). He appeared to those who most needed to see Him. They were the ones who had spent years with Him, watching Him do miracles, watching Him heal the sick, and teaching great wisdom and love. After Jesus died, their faith in Him had been shattered. It was necessary that Jesus appear to them in order to establish the truth of who He said He was; namely, God in flesh (John 8:24,58; 10:30-33).
Fourth, Jesus would have to appear only to those who had seen Him before His crucifixion since appearing to someone who had never seen Him nor knew that He died, would prove nothing. This means that the ones whom Jesus would appear to were those who were following Him in the area of Israel. This further means that at best, other records of His resurrection would have to be hearsay, written well after the fact, by those who did not know Jesus.
Fifth, we do have non-biblical accounts of the resurrection of Jesus.
No sign would be given
Jesus typically would not demonstrate anything miraculous to those who refused to believe in Him. It is, therefore, consistent with Jesus' method to demonstrate Himself to those who were in need of Him and who did not mock Him and doubt Him. Like it or not, this is how He operated. It would be logical to assume that He would deal in the same manner after His resurrection and only appear to those who knew Him and followed Him. For verification of Jesus' denial to those who doubted him, please note the following quotes.
Jesus plainly taught that He would not "perform" for those who denied Him. He did, however, do public miracles in order to validate who He was, God in flesh (John 1:1,14; 8:24; 8:58). This great truth is a matter of faith and is not something proven with a calculator or a camera. Jesus claimed to be the Son of God which, in that culture, meant to claim equality with God (John 5:18). Jesus said that "Before Abraham was, I AM" (John 8:58) a statement that infuriated the Jews who were familiar with God's self description to Moses in Exodus 3:14 when He said, "I AM that I AM. Thus you shall say to the sons of Israel, I AM has sent me to you." It is a claim made real by evidence. The evidence was His miracles.
The real issue of the resurrection deals with its evidence. This evidence consists of the testimony of many people who stated that they had seen Jesus after His crucifixion and death. The same people who testified of the resurrection of Christ also gave up their social and economic security and put their lives on the line in order proclaim that Jesus had risen. Does it make any sense at all to say that they knew Jesus did not rise from the dead and had concocted an elaborate plan in order to deceive a great many people into believing that Jesus had risen? Why would they do that? Does it also make any sense that they would continue in this lie while being persecuted, ostracized from family and friends, beaten, imprisoned, and finally killed for what they believed? It makes more sense to believe that their actions were consistent with their teaching. In other words, they taught about self-sacrifice, dedication to truth, love, peace, etc., and they based it all on the risen Lord. It was based upon the truth that they had seen.