Thank you for using the forum. My name is ***** ***** I hope to assist you today.
These bonds are contracts, much like any other contract, however they carry several guarantees (likely what attracted you to this particular financing vehicle in the first place).
To enforce these contracts when the other party is unwilling to perform their obligations (such as pay out under the bond terms) - like any other contract - you have the remedy to sue them in state court for "breach of contract".
It appears that you have identified the appropriate successor in interest for your bond holder already (the bank issuing the bond closed and was purchased by a subsequent bank - this subsequent bank is the successor in interest and is entitled to any benefits of the contract, as well as liable for all obligations (such as paying out under the bond terms)). You would name this entity as your defendant in the lawsuit.
I understand you are having some trouble identifying a law firm that is willing to handle your case - this is a somewhat nuanced area of law, although it is really not that complicated a case. Most general civil litigation attorneys can handle this kind of matter, but if you can look for attorneys that have some experience with "municipal law" or "government contracts" law experience you will probably have better luck finding an attorney willing to take on the case (I know that there are many attorneys in Ventura as well as in the greater Los Angeles area that can handle this kind of matter - it may take a little bit of work to find one (do not hesitate to turn one down if the first one you talk to willing to take the case does not seem appropriate to you - you are going to be working with this attorney for a long time, do not accept a bad fit simply because they are the first attorney to say "yes", you can always tell them "not right now" and they will always be willing to take the case later).
Short of filing a lawsuit, you can try to mediate the dispute with them - contact your local bar association and request referrals to mediators, a third party neutral can often help you reach a mutually agreeable resolution. Use the bar association's referrals to contact a mediator or two, the mediator will then contact the other party to set up a mediation session, and you can go from there - hopefully resulting in a formal or written settlement agreement, and save yourself the time and expense of litigation.
Your attorney should be able to help you with this process (I wouldn't recommend approaching a mediation on this particular issue without counsel, but you can if you choose to do so).
You can find local attorneys using the State and local Bar Association directories, or private directories such as www.AVVO.com; www.FindLaw.com; or www.Martindale.com (I personally find www.AVVO.com to be the most user friendly).