lost aperture cd - want to install new

Hey there,

I've been using Aperture 3 since early 2010.

I just bought the new MacBook Pro and wanted to install Aperture3 but couldn't find the disk. Still got the whole box with manual, serial number etc. but not the disk. So I wondered how to install Aperture again without buying an extra version of Aperture. Maybe you got some advice for me.

Thanks in advance