According to the State Bar of California, as of yesterday there were 189,709 lawyers who were actively licensed in California and 58,363 who could reactivate their licenses if they wished to do so. https://members.calbar.ca.gov/search/demographics.aspx While you don't have the time or energy to contact all of them, surely there is one hungry lawyer out there who would be pleased to take you on as a client. If the rights you think you have are valuable, and you're at stalemate, it might be a good investment to retain one and then follow his or her advice.Where to start looking?
AttorneyPages.com, or the local county bar association in a major city such as Los Angeles might be a good place to start and there also is the State Bar's intellectual property law section http://www.calbar.ca.gov/Attorneys/Sections/Intellectual-Property-Law/About. Many California lawyers are well versed in copyright law issues and royalty matters, and would be willing to take on private clients who pay them -- even if in the end they say you have no case, or it's unlikely worth your while to proceed. My sense is that while their minimum and hourly charge to review a matter may be even higher than previously suggested -- especially for more experienced lawyers -- some law schools have programs that might also help.