I may be speaking a little out of turn here. I've never used Tianeptine personally. All of the advice I would give is based on what I've read and what I've heard about this drug. It seems like all of the arrows point toward Tianeptine's Opioid-agonist properties as being its reason for use. It sounds like you have already identified this OP, as you're speaking of Poppy Tea as a replacement.
This all filters down to suggesting an Opioid to take its place. Opiods are like liquor, I feel, they produce effects that give each of the drinks their own unique qualities, but at the end of the day, you're drinking it because it contains Alcohol, the rest is not super important in the grand scheme of things.
I see you're in Texas. I'm sure there was a time in which Texas was radically different than other parts of the country in terms of drug availability. Since the beginning of the Opioid Epidemic over a decade ago, Heroin and then Fentanyl have become a part of essentially every urban area in North America. You're going to find Fentanyl for sale in Houston just like you will in Philadelphia. I know some places are all about the pills while up here in the Northeast, it is still sold in branded, stamped bags.
You're options are limited. If I had to make a suggestion, I would suggest Codeine. However, if you're after Opioids in general, there's no reason why you couldn't just obtain Morphine or Heroin and use something like volumetric dosing to make an appropriate dosing scheme. You could obtain Morphine for instance, cut its potency by 10 to make a Codeine-like potency. You could order Heroin and do the same as Heroin is going to be approximately the same potency as Morphine if taken orally, which I assume you do already with your Tianeptine.
We can't tell you where or how to get these things here on the forums. We live in a society in which we all know that drugs can be delivered from the Golden Triangle to your PO box. We can't give you the specific advice required in connecting those dots, though I'm sure you could figure it out.
Opioids are available out there on the street, but I would never advise anyone to go looking for them. They are often tainted with other substances like Xylazine, and in truth, we know very, very little about the composition of this stuff from one day to another.
I'm not telling you do or don't, but be very careful in dabbling with stronger Opioids. Keep your dose as low as possible. Don't mess around with it.