Ghost of Tsushima: Fox Dens in Act 1
You don't have minor charms in stock at the start of the adventure, so you should seek to complete a few side quests in the first place in order to get them. Don't forget the Shinto Shrines for major charms.
Note: You will need to free the village of Azamo to the south for his Fox Den to appear. For that, complete the series of quests of Yuna, then the secondary quests of release of hostages.