You will need to use a software platform that has opening indications if you want to get them all. I use Echo's software which has MDX, which shows all the premarket quotes and literally has hundreds and hundreds of stocks each day that gap up and down. It comes from the ITS system, and starts filling in on some stocks at 20 mins. before the open.
I have heard that AT also has indications, have not seen it myself. What I also do with Echo's quotes is run all the indications into an excel spreadsheet (you can DDE the premarket indications into excel or a Visual Basic program), then send opening orders that are price adjusted based on the premarket high and low open. A great tool, I could not live without it.
Good luck,
Jim