Daniel, as you might imagine the cleaning and staining of keris has been much discussed on this forum. Here's a good thread link, but you might want to search further.
http://www.vikingsword.com/ubb/Forum1/HTML/000717.html
Nope, you won't find Arsenic Trioxide at your corner druggist.
If you search on-line you can find it wholesale to chemical companies. I would try calling one of these wholesalers to find out who they sell to in your area. Then you might me able to convince that local company of your need and they might order it for you. It is obtainable, but it's not easy and it might take time and patience.