I'm a military (soon to be civilian) loadmaster. I believe that many (though not all) loadmasters come from the military.
Im not sure who would conduct loadmaster training in the civilian sector, if they still do at all.
As far as qualifications, physics and maths are probably the most important, and I use both on a daily basis. A good command of the English language and ability to think on your feet are probably the other requirements.
Long days and hard work if you do make it! Good luck anyway.