Your request reminded me of Barbara Tropp's China Moon Cookbook: amazon.com/China-Moon-Cookbook-Barbara-Tropp/dp/0894807544. In her cookbook she has recipes for a couple of interesting oils that might stand in for your vietnamese chili oil.
Searching for a recipe something like hers on the net I found: food52.com/blog/12416-how-to-make-sichuan-chili-oil-from-scratch