California Probate Code section 8221 provides that a will can be proved by proof of the testator's handwriting and proof of the handwriting of one of the witnesses. If you cannot prove the handwriting of one of the witnesses, you can submit an affidavit of a person with personal knowledge of the circumstances of the execution.
You may need to do a little detective work to find the witnesses or the attorney who drafted the will. If you know the name of the lawyer who drafted the will, check the State Bar website to see if s/he is still practicing. The witnesses are probably people who worked for the lawyer at the time (paralegal, another lawyer in the office, etc.).
You might also try the local county bar association. If one of the witnesses was a paralegal or legal secretary, chances are other estate planning lawyers in town know her/him or know people who are friends of his/hers.
It sounds like you're trying to do this on your own. If you continue to run into difficulties, you should consider hiring a probate lawyer to assist you.
The information you obtain at this site is not, nor is it intended to be, legal advice. You should consult an attorney for individual advice regarding your own situation.
I would only add that Section 8221 of the Probate Code does provide that if the will "on its face conforms to all requirements of law" the court may permit proof of the will by proof of your father's handwriting and (b) a document "reciting facts showing execution of the will" by (i) "a writing in the will bearing the signatures of all subscribing witnesses."
To take advantage of this provision you definitely need to consult with a probate attorney.
Mr. Grain is licensed to practice law throughout the state of CA with offices in Los Angeles/Beverly Hills and Pasadena, CA. His phone number is 877-858-4724 or his email address is firstname.lastname@example.org and his website is www.grainlaw.com. Legal disclaimer: LEGAL DISCLAIMER Mr. Fromm is ethically required to state that the response herein is not legal advice and does not create an attorney/ client relationship. Any response is only in the form of legal education and is intended to provide only general information about the matter within the question. Oftentimes the question does not include significant and important facts and timelines that if known could significantly change the reply or make such reply unsuitable. Mr. Grain strongly advises the questioner to confer with an attorney in their state in order to ensure proper advice is received. By using this site you understand and agree that there is no attorney client relationship or confidentiality between you and the attorney responding. This site should not be used as a substitute for competent legal advice from a licensed attorney that practices in the subject area in your jurisdiction, who is familiar with your specific facts and all of the circumstances and with whom you have an attorney client relationship. The law changes frequently and varies from jurisdiction to jurisdiction. The information and materials provided are general in nature, and may not apply to a specific factual or legal circumstance described in the question or omitted from the question. Circular 230 Disclaimer - Any information in this comment may not be used to eliminate or reduce penalties by the IRS or any other governmental agency.