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?
Regs don’t change in 2024. Any (and only) car dealers can provide the credit even if they don’t know it.