In Black Panther (2018), the following event happens
After ingesting the heart-shaped herb, Killmonger orders the garden to be burnt, leading to all the herbs getting destroyed except one. That one is consumed by T'Challa. Hence, as far as what we know, no heart-shaped herb is left. And no other way of gaining Black Panther's powers is shown in the movie.
Given that, has there ever been any mention in the comic universe of an alternative way of becoming a Black Panther?
Erik Killmonger's plan went somewhat differently in the comics. He never destroyed the herb gardens, so the Black Panther legacy was never put in jeopardy. However, there is an alternate way of gaining the Black Panther's powers.
In the comics, Killmonger settled in Wakanda and became an established citizen, then staged a coup while the Black Panther was away on an Avengers mission and ate the Heart-Shaped Herb in order to gain the Black Panther's powers. However, since he wasn't a member of the royal bloodline, his body rejected the herb. He never had the opportunity to destroy the gardens because, well, he went into a coma.
After his recovery, he eventually developed a synthetic version of the herb. This might be the solution they go with in the MCU. T'Challa's sister Suri at one point eats the herb herself, so it wouldn't be surprising if, in the movies, it's she who develops the synthetic.
