Look at restaurant supply stores. The one I use is Cash & Carry. You can get from 1 quart, up to 10 gallon sized containers there (and everything in between).
You can also get food grade storage buckets from most bakeries. They have usually contained frosting, or lard. Wash them out, and you can quiet safely use them. They are often free, but sometimes $1-$2 in price. Most bakeries get 3-5 gallon sized buckets. Don't try to use a bucket that contained pickles as it will make your pasta smell like pickles (deli's also get food delivered in 3-5 gallon food grade buckets).
If you prefer, you can order a brand new bucket, from Emergency Essentials. I would order a Gamma lid as well, as they are easy to open and close. Here's a link:
http://beprepared.com/category.asp_Q_c_E_440_A_c2c_E_ln_A_name_E_FoodStorageContainers
This container holds 2 1/2 gallons:
http://beprepared.com/product.asp_Q_pn_E_MS%20C024_A_name_E_SNAPWARE®%20%202%201/2%20Gallon%20Barrel%20container%20(holds%2040%20cups)
It is important to use food grade plastics, to store your food in. Otherwise you will be exposing your family to some pretty nasty chemicals.
~Garnet
Permaculture homesteading/farming over 20 years
Over 2 years food storage in our pantry (for three adults).
Cooks soups and stews in our 20 quart pot, so I use large containers to repack for storage in the fridge.
P.S. I should have read the other replies first. Do NOT use a bucket from a hardware store! I cannot stress that enough. I am NOT kidding, when I say you will put nasty chemicals in your families food if you do that. The buckets may look the same, but they are NOT the same. The plastic is VERY different. Use a real food grade bucket, not something from the hardware store!