try timertrac.com, timerdigest.com, collective2.com, futurestruth.com. hulbert, striker securities, attain capital, strategyrunner.com, or other sites. They try to independently monitor the performance of many system vendors. At least, you tend to get realistic fills, not doctored up ones like Millennium trading
However, on these sites, there is usually only a couple of useful systems, and they often have a short shelf life. This is the way of system trading. Do a lot of research before trading one.