Question

where did the forest people get their supplies of rice and other grains,

Answer 1

they get it from the forest only

Answer 2

The forest people get their supplies of rice and other grains from the market through barter system of trading.  

Explanation:

In barter system of trading, money was not involved instead people use to buy and sell with the goods which they had. For example if a vendor is selling a bag of rice to the butcher, the butcher in turn will give equal amount of meat to the vendor.

Likewise the forest people get their supplies of rice and other grains by selling the product prepared and manufactured by them.