Have you studied how to work with the elemental of the plant? This is explained particularly in Esoteric Medicine and Practical Magic. In synthesis, the most effective way to work with a plant is by harvesting it when it is alive. When that is not possible, it is best to find the freshest plant we can. In this case, I agree it is very difficult to find asafetida outside of India. The problem with the powders is they are mixed with other ingredients, so the purity cannot be assured. I believe the seeds will be better. Nevertheless, considering that there are other plants that provide the same service, it may be easier to utilize sage, rue, or even sulphur.
“Nothing is easier than self-deceit. For what each man wishes, that he also believes.” —Demosthenes
"Do not worry; cultivate the habit of being happy." —Samael Aun Weor