In the bounty board (right to the Dr's office) you can get a tip of an inmate who has pills, but you can only do it once a day. You can also go to the drug den and fight the bosses and chose to get a pill from them. Those are the most reliable way I know.
Viewing post in 0.1.8 - Kidlat + Transformation Update comments
The step by step of what I did was the following:
1- Talk to Dr Quinn and ask to be her lab assistant.
2-She'll tell you to complete 3 tasks in the bounty board, all I had to do was use a púmp to "milk myself" and then donate it (you can re-roll the bounty board for 1 credit until you get a task that asks for it)
3-Talk to Dr Quinn again about being her lab assistant, and now you can check the bounty board, the last bounty should be a "Special Bounty" that tells you about an inmate that has the pills you need.
4-Go find the character in question, I'm not sure if there's a way to peacefully get the pills, but you can talk to them and then choose to "Attack" if they immediately surrender you can leave, talk to them again and chose to "Attack" again until they fight back
5-Beat them up and you'll be able to get a "Strange Pill" from them, you can now take the pill to the Dr to progress with the story
Hope it helps
I don't think the ones you can make count, as you need new ones that haven't been discovered yet. What I did after that is repeat steps 3, 4 and 5 a few times, each time the story progresses a bit more and eventually the Dr takes you to the entrance of the drug den, once you have that unlocked you can use that instead of the bounty board to get your pills (you get your pills mostly by fighting bosses in the den)