How to get started buying seized vehicles.Is there a website?

Law enforcement agencies generally hold auctions at random times but are usually announced in local or regional newspapers. USA Today used to announce large Federal auctions. Don't know if they still do. There are web sites that sell lists or directories of auctions around the country but I can't say if they are worth the money.

This site is good: https://www.usa.gov/auctions-and-sales

Try searching for "police auction".

Craigslist is always a good start.