What happened at the trading post in St. Johns River to cause a shortage of supplies in the novel, A Land Remembered?

Soldiers purchased nearly everything in the store the week before Tobias arrived. This is not good news, as Tobias was hoping to trade in coon skins for some supplies the family needs. Although there is no flour, salt, or cornmeal, the proprietor does have some gunpowder that Tobias can use to kill wild animals in order to feed his family.