The benefits of ZMA are mainly the fulfill ones Zinc and Magnesium deficiency, athletes being more prone to this, and promote better sleep (zinc). Some B6 thrown in for better absorption, and a mild testosterone increase due tot he synergenic effect of these vitamins and minerals, in there form and amounts.
Unless your looking for that mild test increase, you can easily buy your zinc and magnesium separately to fulfill the deficiencies and get the aided sleep benefit.
You can get a pharmacy to make you a custom formula of ZMA, although this way is usually more expensive.
Or, obviously just buy ZMA pre-made, brand name from a nutritional store from some respected brands like twinlab or biotest.