You should check pinkbike.com their classified section has a ton of TT/tri bikes FS. I recently was doing some consult work and helped an athlete buy a P5d with PM and race wheels for ~ $5k off of there Brian Stover USAT LII Accelerate3 Coaching Insta
I would advise against Pinkbike.com. That site is riddled with scammers. I was scammed in a bike using all of the correct channels. Luckily the supposed bike was delivered to a commercial address and the box was never found. I made contact with seller nice and he went cold after that. The day after his account was labeled as a scammer.
Was in talks on a second bike but did not pull the trigger. Two days later his account was labeled as a verified scammer.