When will the NFC replacement part be available for purchase?

Ronni Renee, this is the repair forum for helping people with their devices, and the iFixit Store personnel that you need to talk to don't tend to hang out here. You'll have much better luck using the FixBot assistant to contact them or email them at support@ifixit.com

That being said, my guess is the parts aren't available from Google yet, since the phone is so new. iFixit can only sell parts if they can get them, so ultimately it's up to Google whether they are in stock or not.

Out of curiosity, why are you thinking an NFC part needs replacing? The phone's not yet a year old, and I know Google has at least a 1 year warranty, so if it was my phone I'd be checking to see if is covered under warranty first.