Getting references after a company closes after 15 years as a call-centre agent

The company closed and I am not sure how to reach former colleagues. I am in Louisville, in case local advice matters. I have one former client who liked my work. How do you ask politely?

I kept a note of my results so my references could be specific. They appreciated it.

Ask former colleagues and supervisors in a short message and give them a summary of the job you are applying for.