Well that sounds interesting! Further perusal suggests its a Chinese herb...., from below I cannot determine if its a Traditional herb.
"Securinine is the major alkaloid natural product from the root of the plant
securinega suffruticosa. It was originally discovered over 50 years ago and reported to have potent biological activity
[5]. Though this compound has not been utilized in the United States, it has been used clinically in several other countries particularly China and Russia. In China it is considered one of the 50 fundamental Chinese herbs and is used in Chinese herbal medicine
[6]."
This would suggest one could get it: at a traditional Chinese Herbalist...(however, the statement it was "discovered" 50 years ago is not consistent with it being in the CTM protocols). Can't check on that at the moment...
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3123298/