Crypto derivatives were naturally discovered as an interesting addition to cryptocurrency exchanges first – probably as individual contracts between interested investors on these exchanges. Nowadays, there are already a couple of exchanges that offer crypto derivatives trading as a standard feature: BitMEX is the current market leader, according to The Merkle News; others are OKCoin, Crypto Facilities, Coinpit, and Deribit, as well as LedgerX (the first regulated cryptocurrency exchange in the US).
There are dozens, if not hundreds, of unregulated online exchanges and brokerage firms offering cryptocurrencies and cryptocurrency trading products. Investors should be wary of too-good-to-be-true promotions and promises of quick riches. Once you deposit money, many of these firms will charge you outrageous commissions or make it very difficult to withdraw funds. Some of the worst offenders will simply steal your money.
Note that you could just keep bitcoin on CryptoFacilities waiting to make the trade so you don't have to wait to move the bitcoin you bought over. This is called see-saw arbitrage model, where you keep funds on both exchanges to avoid having to wait. This is fine, but you can't ignore that there is extra capital being used in the play, so it affects your rate of return and capital utilisation. We will not use this method, we will do a full, complete, legitimate arbitrage process.