From GameWatcher: “Monster Hunter: World is currently bringing back a seasonal event per week, letting players earn items like the Black Crystal Ticket once more until the end of August.
As you can probably tell, Black Crystal Tickets can be earned by completing a particular event quest called A Flash in the Pan. It requires a Hunter Rank of 6 and pits players against three Tzitzi-Ya-Ku monsters in an Arena fight.”
Source: N4G PC Monster Hunter: World Black Crystal Ticket