Does Acacia confusa perhaps occur in Korea? Are there any Desmodium species (or Codariocalyx motorius)?
There's surely Phragmites australis to be found somewhere - that's pretty much a ubiquitous species. There are likely to a number of other grasses with some level of interesting alkaloidal content - wikipedia (https://en.wikipedia.org/wiki/Category:Flora_of_Korea) lists Phalaris arundinacea as occuring in Korea so you should familiarise yourself with the genus Phalaris as well.
The best thing to do is familiarise yourself with Korean flora through the literature while getting to grips with which species and genera show promise in this direction. That should help you get some idea where to look. Another area to look into is traditional herbal medicine.
For the longer term, it should be relatively easy to obtain seeds of some active Acacia species and grow your own.
https://www.nhbs.com/3/series/flora-of-koreaQuote:Please note that we have spoken to the publisher in April 2017 who explained that national regulations prohibit them from selling these books. However, the National Institute of Biological Resources, Korea, makes these books available for free for museums and librarians, and we advise these customers to approach the institute directly.
“There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli