It's your job to force the other party to turnover tax returns and bank records. If there is a court order to pay child support he must pay until its changed. You can ask the department of child support services in your area to help. You might even be able to open a complaint against him on-line.
It would likely be helpful for you to contact the local office of the Department of Child Support Services because they can assist with enforcing child support orders. You can find out more about their services online here: http://www.childsup.ca.gov/Resources/ApplyForServices.aspx
Also, because you stated that you are not able to hire an attorney for this matter, you may want to seek assistance from your county's Family Law Facilitator so they can try to guide you; although you would still be representing yourself. If you are in Contra Costa County, then you should check here for information on such services provided through the local court:
Legal disclaimer: The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change.