Go to
www.acmaxx.net. They have 5dmkiii lcd screen protector made of hard poly-carbonate with UV low reflection coating. It's better than glass or plastic ones.
They dont sell direcly, but tell you where to buy depending on where you are living (including Ebay).
I have them on my T1i, 50D and 5D MKiii; all were bought from Ebay.
They are good ones to protect your investment.