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=1467939.0

It 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.