Galarian Zigzagoon wil be given out to participants at the Champions League 2021 Yokohama event, that is being held this weekend on October 3 and October 4. It was silently revealed on the livestream page where the event will be livestreamed.
For more info about this event, you can look it up in Japanese on the official webpage:
Update 3-10-2020: The card is selling now for roughly 5500-7000 yen in Japan on auctions, there is a high demand for this card.
Galarian Obstagoon is a playable card, due to it's limited availability, and being the only Galarian Zigzagoon with a holofoil treatment on the artwork and having a unique stamp, that could be the reason for this price.