I disagree...
You said, "Don't say the Gospel writers " which eliminates all testimonies... so I think it was very applicable.
The Gospels aren't eyewitness accounts, though. That's the point.
Peter was a witness:
1 Peter 1:3 Blessed be the God and Father of our Lord Jesus Christ, which according to his abundant mercy hath begotten us again unto a lively hope by the resurrection of Jesus Christ from the dead,
1 Peter is pseudipigraphal (ie not actually written by Peter). You know this is the consensus of NT scholarship, yes?
Paul knew he resurrected 1 Corinthians 15:12 Now if Christ be preached that he rose from the dead, how say some among you that there is no resurrection of the dead?
Paul never says he laid eyes on Jesus while on Earth at all. He converted to Christianity because he had a vision of Jesus already being in heaven. So that isn't an eyewitness by any reasonable definition.
Peter preached it: Acts 1:22 Beginning from the baptism of John, unto that same day that he was taken up from us, must one be ordained to be a witness with us of his resurrection.
Acts wasn't written by Peter. It was written by the same person who wrote Luke. And suffers the same kinds of fundamental problems the Gospels do.
Matthew acknowledged it: Matthew 27:53 And came out of the graves after his resurrection, and went into the holy city, and appeared unto many.
Matthew's author is anonymous.
The whole 130+ in the upper room believed he rose from the dead.
Your only source for that claim is the Gospels.
and all the other statements that convinces the 3,000 on the first sermon and 5,000 later on. It didn't start because there was still a body in the tomb.
Your only source for that claim is the Gospels.
The "outside support" is just to give auxiliary support to what happened.
But they don't. None of them were witnesses to anything that happened to Jesus. They simply reported what was alleged by Christians at their time.
So... back to, "if you don't want to use the eyewitness accounts, what do you want us to use?"
Actual eyewitness accounts that aren't full of completely absurd claims would be a good start.