It is always better to take natural form of vitamins rather than vitamin supplements from the market because they are fresh and free from any side effects. The main dietary sources of vitamin C are fresh fruits and green leafy vegetables. Traces of vitamin C occur in fresh meat and fish but scarcely any in cereals, Germinating pulses contain good amounts. Roots and tubers contain small amounts.
Amla or the Indian gooseberry is one of the richest sources of vitamin C both in the fresh as well as in the dry condition. Guavas are another cheap but rich sources of this vitamin. You can look for more at http://www.healthvitaminsguide.com/vitamins/vitamin-c.htm . I think this may help you. Also there are many other educational health sites with lots of information on this.