Most of the rather open DNMs have been seized by LE or are suspected of being seized by LE and only still operating to gather evidence.
If you want to buy off the darknet, you'll have to find either a forum based market or just the contact details of a dealer and contact them directly.
Other than that, you're gonna have to find a connect IRL.
Other options include breaking a tooth, letting it get infected, and then having an emergency extraction done, thus getting pills to manage the pain of the healing wound, or develop bronchitis and going to an urgent care clinic. Odds are they'll prescribe you an inhaler, a steroid, "cough pearls," and Tussionex (like codeine/promethazine, but hydrocodone and chlorphenamine). With Tussionex though, it's very hard to get high w/out experiencing the bad side effects of chlorphenamine. Odds are you'll probably end up feeling like you just downed a bottle of DXM or DPH instead of the euphoria of an opioid high. The chlorphenamine isn't really there to help with anything, it's just there to discourage abuse.