Lists of β-carboline alkaloid source plants are out there for the finding - even a little dedication and effort will be rewarded with knowledge. Whichever plant may turn out to be the most practical, or the most rewarding, depends on your situation and your capabilities.
Blackcurrants are more likely to be of use than tobacco where, afaik, harmalas are trace products of pyrolysis for the most part. Some rustica tobacco may be richer in suitable alkaloids but there is always the problem of nicotine being dangerously toxic, not to mention physically addictive.
If you are somewhere where Syrian rue is remotely accessible, just use that - I've struggled to cultivate it, however.. Otherwise, consider growing caapi. If you have a lot of temperate outdoor gardening space, it may be worth getting to know sea buckthorn (
Hippophae rhamnoides) or/and various of the
Elaeagnus species, e.g. Russian olive or autumn olive.
“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