dose anyone know where i can find a thick exhaust manifold gasket? something like 3mm thickness>?

yeah three normal gaskets i don't know. unles you get some gasket material and make ya own

machine the manifold as a thicker gasket has more surface to start burning through some times its cheaper to do it once not 10 times!!!!!

Why ??? In most cases you only require copper silicon .. Just drill out the outer holes on manifold to allow for expansion. Just let the centre two hold it in position... Then if you still have issues? Just cut between each port on flange 3/4 way through [ from top to 12mm from bottom] so it cannot twist / warp ...