Place pork, fish sauce, and coconut soda (or coconut water plus sugar) in a medium heavy-bottomed Dutch oven over medium heat. Bring to a bare simmer, reduce heat to medium low, and cook, covered, for 30 minutes.
Remove lid, stir pork, and add 1 to 2 cups of water, as needed, to bring liquid just 1/3rd of the way up the pork. Return to medium-low heat and cook, partially uncovered, until pork can be easily pierced with a fork but still retains some resistance, about 1 1/2 hours.
Once pork is tender to your liking, uncover pot and increase heat to medium, then add garlic and hardboiled eggs. Simmer the sauce, stirring frequently, until the garlic loses its raw aroma and the eggs gain some color from the liquid, about 10 minutes. Taste for seasoning and add fish sauce and sugar as needed, as well as additional water if desired for a looser consistency. Serve over steamed rice with sliced chiles. The stew will taste even better the next day.