how to force an attorney to return my papers?

Your new attorney should be able to get everything for you and even if don't have a new attorney, if you've paid your bill, your previous attorney by law can't retain your case files. I also believe that even if you didn't pay his bill, he is still supposed to return your files, although I've heard that some attorneys will charge a fee to make copies of case files on unpaid accounts.

If your divorce is still in court, I'd tell the judge and see what the judge advises you to do. Your could also report him to California Bar Association by filling out a complaint form or calling their number to talk to a representative.

You don't say where you live, but somewhere look for the address of the local Bar Association, write, don't phone, by registered letter explaining the position.

Could start here, I assume you are in the USA.

http://www.abanet.org/