You can buy Vitamin C in most drug stores and supermarkets.  Costco has a
good supply at wholesale prises:
Vitamin C with Rosehips,  500 tablets of 1000 mg , $9.99
Chewable Vitamin C, 300 tablets of 500 mg Sodiume Ascorbate, $9.99
Ester-C, 300 tablets of 500 mg Calcium Ascorbate, $16.99
A fairly good mail order supplier is:
Wholesale Nutrition
Vitamin C is acidic, and may upset stomach if taking large amounts.  
Sodium Ascorbate is neutral, and is the best for taking large amounts to
combate virus infections.
Calcium ascorbate supplies 10% in weight of water soluble calcium which is
needed to build bones.  10 grams of calcium ascorbate is the best daily
supplement to maintain optimal health.
As a public service, Offete Enterprises distributes sodium ascorbate and
calcium ascorbate from manufacturers.  Prices are reduced recently.

Sodium Ascorbate USP 99.9%, $8/lb
Shipping $5 up to 3 pounds

Calcium Ascorbate USP 99.9%, $8/lb
Shipping $5 upto 3 pounds
Mailing Address:

Offete Enterprises
156 14th Avenue
San Mateo, CA 94402
Tel: (650) 571-7639
Fax: (650) 571-5004

eMail: support@offete.com
Buy Vitamin C