You usually have to buy one off someone. I don't know of any free bot traders.
There is information about one you can buy in this thread.
https://bitcointalk.org/index.php?topic=1467939.0It has a demo you can try for free, but the demo won't let you log into an exchange and do real trades. I don't know if it's profitable or how buggy it is besides a bug trading on Bittrex on OS X.
Bots are not ment to make you profit that is your job. The not does not think you do. The not just makes sure you dont miss any trades , for example while you are asleep. Because we can't be at our PC 24/7 watching the market. Bots are not magic computer programs that generate you profit.