The IRS has a web site for dealers to register:
After Jan 1, I want to buy a used EV from a dealer who has registered so that I can get the $4,000 credit immediately and not have to wait until I file my taxes the following year.
Is there a way to search for dealers who are participating?
I wouldn’t worry about it for 2024.
Dealers are going to be claiming the credit for themselves, and then passing it on to you via a discount. This is money in their pocket. Dealers are not going to pass up free money. It may be a bit rocky in early Jan as the system works the kicks out, though.