By quoting the tweet and including the twitter handle of each follower account you want to see the tweet in your quote. It is not easy as it would require you to type in the twitter handle of each account, but it can be done.

Don't think I want to enter 400+ followers in my tweet; guess I'll just use hashtags.

since the new Twitter, I can't find my followers. I Googled and it said to click on lists. That's empty. I found links from search to click on "following list", and that works, but it says it's supposed to be available from my profile. There is little available from my profile.

The new Twitter is a complete failure. Seeing new Tweets isn't a static link, it disappears. The links don't scroll the same.

It's 50% of the old Twitter. Fail.

Since they are not your followers, you cannot send top-level or thread-starting tweets to them. You can only do that to your own followers.

You can post a response to a tweet of the desired account. This will go to all of the followers of the top-level tweet. Keep in mind that if your response is not addressing topics in the tweet you respond to, your response will probably be flagged as spam.