I have looked for options in the past too. Unfortunately no such legit sites exist. Even if you are able to buy an option for bitcoin, which I doubt anyone would offer, then being paid out if you were to earn millions from it is unlikely. Also the options for bitcoin offered will be very short term, from a week or 2. Over a month is too risky for any seller.
Currently on
www.deribit.com you can trade (vanilla european style) options up till 3 months out (quarterly). In the market you can either buy or sell, as an example..the current market for a 30 september 700 call is 42dollar bid - 46 dollar ask. Though you wont be able to do huge quantities on those prices, as the market is still not very liquid. (marketmaker is quoting for 2 options on all strikes, after that quote becomes slightly worse., though bigger trades can be negotiated of course in the chat, or by simply placing your bid/ask in the orderbook.