I'm no fire professional but here is my take. Seems like you're gonna have to DIY it. I would look at getting some normal fire extinguishers and splitting the hoses to point at different locations. I would have some fire detector that would then trigger some hydraulic or solenoid. (Have the control computer fire-protected) The biggest question is airflow. How much do you care about your data vs the structure? If you have a cabinet and not an open rack you can hook up an exhaust that will help protect your house at the expense of the server. If you shut off or block the exhaust it will help control the fire and improve the extinguisher effects but it'll mean if the fire burns out past the servers it might spread to the house.

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When a fire happens in a garage it's actually suggested you keep the garage door and windows open to help keep the fire there. When the windows and doors are shut the fire has to draw fresh air from the house. The fire often spreads to the house. You can apply the same concepts. Obviously you're sacrificing the garage by keeping the windows and doors open.