Coins on local bitcoin.com placed there by other individuals like you and I who wants to sell their bitcoin for cash and at their own different rates and medium currency they want to accept. That coin comes directly from other parties.
The others are called exchanges or (sellers)
They have the bitcoins for sale at 1rate a point in time.
You go there and buy, very simple.
Not all exchanges trade coins. Those that trade eg. Binance, huobi, bittrex, etc.
Those that do not trade are very few and mostly found in your home country which accepts your home currency.
Eg of my home exchange that do not trade is Payplux.Com