That's against the law. It's called conspiracy. And that's when two or more people plot to commit a crime in the future. You are entitled to have your own opinion. And you have the right to assemble with others to express your opinion. But if you assemble to harm others or break either state and or national constitutional law, that is a crime and it is actually possible to be charged and imprisoned for conspiracy to commit an act of terrorism, which is a federal offense. I understand that many people don't like the law and the enforcers of the law. And you should express your opinion. But I wouldn't even dare mentioning anything that has to do with plotting against any police or law enforcing agency. The government doesn't screw around when it comes to stuff like that anymore. If you continue to talk like you currently are, it is possible that the government will send a private-eye from either a state-wide or possibly even federal agency to investigate you. And if they deem you a threat to national security, they will prosecute you.
The best route for you to travel is to demand internal reform within the police agency from your elected officials. Because they are the heads of all the government workers, including police officers. And your elected officials, depending on the position of the official, do have the power to reform personnel and mend laws.
As far as a website that has the purpose of what you're seeking, I haven't heard of such a site. You might have to create your own.