[A. G. Maisey]

Yes Giovanni, the availability of materials at times in the past could have been a factor, however, perhaps not as great a problem as we might think. In Bali the Pandai Caste was and is powerful within Balinese society. The members of the Pandai Cast are workers in iron, and they are spread throughout the Balinese society. There were long standing trade links with China, there was iron smelting going on in Jawa, and I think probably Bali too, at least the beach sands in many places would seem to be suitable for production of iron.

So, yes, material could have been a factor, but perhaps not quite so much as we might think.

EDIT

Something we must always remember in this context of availability of any type of materials to areas of SE Asia is that there was a well established trade network throughout SE Asia, and even as far as Madagascar, China, and interestingly, Northern Australia, that in some cases extended back as far as the 2nd and 3rd centuries AD. There was nickel bearing iron being exported from Luwu in Sulawesi from at least the time of Majapahit.

SE Asia may have been unknown territory to Europeans prior to first contact, but it was certainly no unknown territory to the people of India, China and the Middle East, let alone the people of Maritime SE Asia.