There is methadone in Bali, or methadon is it's known here. But is it practical? No not at all. Sangli comes up in my searches, though they do date back a few years as having a methdon klinic. Now you will need a reference from your western dr to go on it, then you will need to pay out of pocket piss tests, register at hospital, daily doses. The piss test needs to come up not full of benzos and illict shit, or if it does you need to be able to explain it.
Now, that is the easy bit. The hospitals here are busy as, you need to come at 7am take a ticket, expose yourself to covid and watch a lot of sick and dyeing indonesians, maybe around 2-3pm they will call your number to dose.
Having done the dance for smashing my back and addictive pain medicine, and wheening my way out of the system, bali is not the right place for this. You will have no issue to get scripts for valium xanax (and those tablets fuck you up anyway, I don't see any long term benefits to taking them, I am really proud Ieft them behind) etc here, but hardcore opiates almost don't exist, stock issues etc. Many of the western everyday pharma doesn't exist here or is impossible to get, so I'd suggest if possible to taper/lower your dose and re assess.
It's most likely not what you wanted to hear, but save yourself a very uncomfortable time. Very much old religious values and the pharma pumping world in western, doesn't really exist like that in Bali.