The forum didn't exist when that conversation was happening. I've always assumed these discussions were via email or some other medium. There aren't any transcripts that I'm aware of.
Especially because those conversations didn't exist at all or at least not like described. There is no particular reason to believe Cryddit was telling the truth, especially because a simple glance at original release demonstrates that he was wrong about a lot.
See:
https://www.reddit.com/r/Bitcoin/comments/e9v48b/how_can_sirius_claim_to_be_bitcoins_2nd_developer/falysvv/