If you were hit by a drunk driver how do you find out what insurance company he has?

It will be on the police report. If for some strange reason there is no report, then ask the police to help get this info from the drunk. You might also contact your states dmv some of them have this info (will need vehicle info), file the claim with your company and they can handle your damages etc, and will find out his insurance company, because they will lood to them for repayment.