CBOE Options Chains (delayed)
http://www.cboe.com/delayedquote/quote-table

CBOE Options API/subscription (by tick, real-time)
https://datashop.cboe.com/option-trades-subscription

CBOE Markets Dashboard
http://www.cboe.com/quotes-data/mktquote

NASDAQ
eg (https://www.nasdaq.com/symbol/msft/option-chain)

TD Ameritrade trading API
https://developer.tdameritrade.com/option-chains/apis

Market Chameleon (delayed)
eg : https://marketchameleon.com/Overview/MSFT/OptionChain

Yahoo Finance (delayed)
eg :  https://finance.yahoo.com/quote/SPY/options?p=SPY

Optionistics http://www.optionistics.com/quotes/stock-option-chains