Have a Mac (screen number one) and a displayport output to projector (screen number two). This setup currently works well.

I now need to connect another screen for another display (screen number three). Is there such a thing as a dual-output Displayport adapter so that I can run three screens from a Mac? I know virtually nothing about Macs, so unsure if this is even possible ) The screens are NOT mirrored (ie they need to display different data on each).

There is about 15-20m of VGA cable from Mac to projector, and will be about the same between Mac and screen number three.

Or should I be looking at another option?

Cheers,
Mike.