Getting references after a company closes - what worked for you?

The company closed and I am not sure how to reach former colleagues. I have read a lot of threads here and could not find my exact situation. I have one former client who liked my work. Who did you use?

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

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