True, those sites are great but they aren't official. I think most of them come from 1 or 2 companies (Southern CA and FL IIRC) under a bunch of domains skinned a bunch of different ways. I used to work for a nissan performance parts place and they were asking me to make them their own site from the parts diagrams they got from disk through some agreement they had with Nissan as a service department IIRC. (a little over 10 years ago)
I'm not sure how all of them work but mopar the dealerships decide if they want to be part of it. If they do then the website is already made and maintained. If somebody buys parts off of it they will direct the sale to a given dealership based on some criteria I don't know. Maybe just whats closest and in stock according to their inventory.
Anyways, official sites:
* https://store.mopar.com
* https://parts.ford.com
* https://parts-catalog.acdelco.com
I'm not sure how all of them work but mopar the dealerships decide if they want to be part of it. If they do then the website is already made and maintained. If somebody buys parts off of it they will direct the sale to a given dealership based on some criteria I don't know. Maybe just whats closest and in stock according to their inventory.