Not sure what you consider best, but I assume price is a big factor. *Just noticed you wrote online but I'll just keep everything I have here.

You might find a used phone section in your local thrift shop.

Someone is probably selling new and used flip phones on kijiji, ebay, fb marketplace etc.

For buying new, Best Buy is available nationally. I've seen refurbished phone shops but most carry only smartphones. Wireless carriers can let you buy phones outright with no plan but they are overpriced.