Toyota Celica vvti exhaust manifold spring and bolt threads

[tjhibbyvti]

Does anyone know what has happened to my exhaust manifold thread on one side for the bolt and spring , last year my local garage fitted a hellicoil to either the left or right side after it stripped after putting on my aftermarket stainless steel exhaust , after taking it off last week and then putting on the original for the MOT then taking it off again to put on the stainless steel one again one side only tightened up so far so I  took it off and noticed the threads were stripping , then I noticed there were nothing there to screw the bolt into just a thin plate with nothing behind compared to the other side which I could see the threaded length behind it , does anyone know what's happened ? Also where can I get new bolt and springs from  ? Help much appreciated at this time.