An agency as large and corrupt as this one will think very little of your complaints, typically doing exactly nothing with them. Nor is it likely that in a city that dangerous with that much corruption that any government agency with oversight will step in on the behalf of any open carrier, even if he or she gets the **** beat out of him or her. Showing up in large groups will similarly do nothing, other than probably ensure the safety of that group on that day.
The one and only option that will be taken seriously is law suits that are aimed not only at the agency, but individual criminal officers as well, and even their supervisors. I suggest federal law suits managed by the best attorneys you can find. File them often.
In order to do a good lawsuit, off the forums, and if possible even not involving any form of electronic communication, OCers in areas like this need to set up investigations utilizing hidden cameras, freedom of information requests, and "stunts" where you film people who go into areas knowing they will get abused by police, then getting them to run their mouthes and admit to crimes which is usually the easiest part. Most of these things should be kept as quiet as possible, only being shown to those who are involved, and to the excellent lawyers you'll need to help you. I would also suggest that only people who have known each other for years and are exceptionally sure that those involved are not government agents should work together. I also suggest never ever making this information public, until after it gets used in court, at which point it will become public anyway.
It takes years of hard work, dedication, and a lot of money or friendly to the cause legal council to remedy situations like this. And even if lawyers volunteer their services, they will likely not spend their own money to file the suit.
The only other option is getting intensive positive national media attention which shows you to be the freedom fighters taking on the abusive criminal cops. And that is about as likely as California adopting 10th amendment gun soveignty within a month.