Is the goal to stop the flow of beer to the taps? If so, just remove the disconnect from the post. Any hardware based solution needs to be stainless to prevent corrosion and contamination, and even then it is iffy. I think stainless beer line valves start at around 23 bucks each and will need fittings to work them in to the system. Google beer line shut off valve and hit the second result (i'm not sure on the rules to posting links here).
Hope that helps.