Not about keris, but while we are in this topic, I think I'll include this discovery as well.
Iron smelting site in Peninsular Malaysia dating 3 - 5th CE. Artifacts that had been found include 1.7 tonne of iron slag, 800+kg of iron tuyere and 150kg iron ore.
Research paper entitled "THE ANCIENT IRON SMELTING IN SG. BATU, BUJANG VALLEY, KEDAH"
http://www.cuhk.edu.hk/ant/Postgradu...kmaMOKHTAR.pdf
The following is a documentary about Sungai Batu. It is in Malay, but it have a reasonable English subtitle.
Very interesting as this civilization is actually older than Angkor Wat where some sites may go back as old as 500BC. 2500 years old.
https://www.youtube.com/watch?v=5oAbe-mKxSE