This is less useful since Zero already answered, but you can check out
http://erowid.org, specifically:
http://www.erowid.org/psychoactives/psychoactives.shtml Herbs and Plants and would be particularly useful. Perhaps you can find something that would work in a manner similar to ecstasy that occurs naturally? However I would be careful to cross-reference whatever plants and herbs you find on those lists to a canine toxicity list, since a canine might be highly sensitive or even poisoned by some of those same things humans use to achieve a high. ;D
For example, this is just me browsing the list, but I see:
- Herbal ecstasy (this is actually under "Smart Drugs" but it seems to be a mix of caffeine and ephedrine, still something that would need to be synthesized)
- Ayahuasca, which seems to be a sort of tea brewed in south america! If you can find a reason why some of the ingredients would be floating around, you could synthesize this since it would not require a laboratory or heavy skills.
- Salvia (listed under Morning Glory). This would be the seeds of the Salvia plant, they're something of a rather short-lived, very powerful hallucinogenic, iirc.
etc, etc, etc. There are tons and tons of naturally occurring chemical compounds that could have effects similar to ecstasy if that's not a viable option in the 'Soulsverse. :o