Getting references after a company closes - first time posting

The company closed and I am not sure how to reach former colleagues. There are 8 people counting on me, so I am trying to be careful. HR only confirms titles and dates. How do you ask politely?

Thanks for writing this out. I went through something close to it last year, and it settled down once I kept a simple log of every call and form.

A client reference worked well for me. It shows you deliver outside the company too.