Short answer — you can buy calming/anti‑anxiety dog foods and calming supplements at your veterinarian (especially for prescription diets) and at major pet retailers and online stores. Below are common product types, example brands, and where to buy them.

1. Prescription “calming” veterinary diets (vet/clinic or retailers with vet authorization)

• Examples: Royal Canin Veterinary Diet Canine Calm (veterinary‑exclusive formula with hydrolyzed milk protein & L‑tryptophan) and Hill’s Prescription Diet i/d Stress (anti‑stress formula for stress‑related digestive upset). These are usually sold through your veterinarian, veterinary clinics, or retailers that accept vet authorization. (royalcanin.com)

Where to buy: ask your veterinarian (they can sell or prescribe), or look for the product at Petco, PetSmart, Chewy or Amazon — some listings require vet authorization or are sold only in clinic channels. (petco.com)

2. Over‑the‑counter daily dog foods formulated to support calm behavior

• Example: Purina Pro Plan Calm & Balanced (formulated with omega‑3s and brain‑supporting nutrients; Purina reports behavioral improvement when fed daily over weeks). These are available without a prescription from Purina, Chewy, Amazon, Walmart and other retailers. (purina.com)

3. Calming treats & supplements (fast acting or situational use)

• Examples commonly used: VetriScience “Composure” calming chews (vet‑recommended/clinically studied chewables) and Zesty Paws Advanced Calming Bites (melatonin/ashwagandha/chamomile mixes). These are sold widely at Amazon, Chewy, Walmart, pet stores and some vet clinics. VetriScience advertises a fast onset for situational anxiety; Zesty Paws is a popular OTC calming chew. (amazon.com)

4. Where to shop (quick list)

• Veterinary clinic / hospital — best place for prescription diets, tailored advice and vet authorization.
• Brand websites — e.g., Royal Canin, Hill’s, Purina for product info and retailer locators. (royalcanin.com)
• Major online retailers: Amazon, Chewy, Petco, PetSmart, Walmart — convenient and often offer autoship/subscribe options; some prescription items may need vet approval. (amazon.com)

Quick practical tips

• Talk with your veterinarian first, especially if your dog has health issues or you’re considering a prescription diet or medication — a vet can rule out medical causes and recommend the best approach. (akc.org)
• If you switch foods, transition gradually over 7–10 days to avoid GI upset. (Manufacturers and retailers give transition guidance.) (walmart.com)
• For situational anxiety (thunderstorms, fireworks, vet visits) you can try a fast‑acting chew or supplement; for chronic anxiety, consider a veterinarian’s behavior plan that may include a calming diet plus training/therapy or prescription meds. (amazon.com)

If you want, I can:

• look up specific retailers near your ZIP code (or local vet hospitals that stock prescription diets), or
• compare 2–3 specific calming formulas or supplements side‑by‑side (ingredients, cost, and where to buy).

Which would you prefer?