You can buy uncooked rice from grocery store. Asian grocery stores usually carry short grain rice (also called sticky rice, sushi rice) which Koreans and Japanese eat. Not all western grocery markets have this kind.
You can buy instant cooked rice from Korean markets. They come in 1 serving plastic container you can microwave for 2 minutes.
The best way to store cooked rice is to freeze them in a tightly sealed bag. If you don't have a big family you can freeze them in small portions. Then, you can microwave it for a few minutes as needed. To make sure rice doesn't dry up when reheated, place the frozen rice in a bowl, sprinkle with some water and cover with a lid or a plate when microwaving it.