IET manufactures the GenRad and QuadTech 1863, 1864, and 1865+ megohmmeters designed to meet most high resistance measurement needs. These megohmmeters with a range of up to 200 teraohms have a history of proven reliability and utility. They are widely used in the aircraft industry among many others.
Let us know what your megohmmeter requirement is and we will find you a solution.