You might try looking at freelance positions that don't mention that they are for a ghostwriter. That's how I did it, anyway. My part in it is really supposed to be confidential, so there was never a 'ghostwriter position' announced.
What did they look for? Work they wanted to edit (with me) and use. My actual job history didn't matter as much as what kind of work I could write. So it came down to expertise/quality/ability but not so much my publication experience. I hope that helps
I really don't know how it's usually done.