looking for group tour that includes underground colosseum

Look at the takewalks website. Specifically their premium Colosseum, Roman Forum and Palatine Hill walk.

Friends took it 2 years ago, loved it. I have no personal experience with the company.

https://www.walksofitaly.com/rome-tours/colosseum-underground-tours/
Very limited dates

https://citywonders.com/rome-tours/colosseum-underground-tour

https://www.coopculture.it/en/products/full-experience-ticket-with-access-to-the-arena-of-the-colosseum/

https://theromanguy.com/tours/italy/rome/colosseum-dungeons-tour-with-roman-forum-palantine-hill

These are very difficult tickets to get. The method for releasing tickets changed and all the tour companies are struggling to get tickets for these tours. Good luck to you.

Also:
https://www.coopculture.it/en/products/full-experience-ticket-with-access-to-the-arena-and-underground-of-the-colosseum/

https://www.coopculture.it/en/products/the-wonders-of-the-colosseum-visiting-the-underground-and-the-arena/

But as Carol mentioned, tickets for the underground are REALLY hard to get. As well, just because some companies are selling tours which include it doesn't mean THEY can land tickets so we've seen a number of cancellation reports.