It should be possible for people to sell a port's production goods (Selling food to food port) when it's stock becomes too low, like Goroum.

100M or less, sell price - 1 = buying price.
50M or less, sell price = buying price.
25M or less, stops selling and will only buy.

Like how you can fish in a food port and sell them right away to restock.

Once plantations arrive things should balance out