Purchasing codeine from unauthorized sources or "online pharmacies" that do not require a prescription is illegal and can lead to criminal charges.
Once prescribed, you can fill the prescription at any licensed retail pharmacy, such as CVS Pharmacy, Walgreens, or Rite Aid. Risks of Buying Without a Prescription where do you buy codeine
In the United States and many other countries, and cannot be legally purchased over-the-counter or through unauthorized online vendors. Legal Requirements such as CVS Pharmacy