You could try to buy a boxed retail version of Aperture on CD from Amazon or Ebay, if they are still available. This will probably give you Aperture 3.1. Then upgrade from Apple's Support page to Aperture 3.4.5.
Only the retail version will probably be much more expensive then the current Aperture 3.5 version from the AppStore.
I would not dare to give any guarantees.
The recent raw support versions were updates to the versions of Aperture and iPhoto, that had been released for the current MacOS X:
See for example the release notes for the latest Raw Support: http://support.apple.com/kb/DL1706
Mac OS X 10.8.5 or later
Mac OS X 10.9 or later
And look at the Mavericks Raw Support page: http://support.apple.com/kb/HT5955
* Aperture version 3.4.5 or later, or iPhoto version 9.4.3 or later, is required to install this update.
With Lion you will definitely be left out from new raw supports.
And I am no longer sure about Aperture 3.4.5 either. Aperture 3.3. worked well with Lion, but you need to check on the Support page, when the Maintainance is over, which Aperture 3.4 version will work with Lion.
Right now I cannot reach the Apple Server - the Downloads page is unresponsive: http://support.apple.com/downloads/#Aperture
Now I could check again So with the latest Lion you will be fine with Aperture version 3.4.5, only no longer with new raw support updates.
OS X Lion 10.7.5
OS X 10.8.2 or later
I have iPhoto 9.4.3 installed. I am not aware of any Apple program that requires Mountain Lion to work rather than lion. Also both Aperture 3.5 and especially iPhoto 9.5 are very minor upgrades. So if new Raw support in both Aperture and iPhoto requires Mavericks then that is a bummer. However I find it difficult to believe that Mountain Lion users will have access to Raw support that Lion users will not. I also believe Apple will likely support future support for non-Maverick users using iPhoto. If they do not do the same for Aperture presumably one can use iPhoto to convert the Raw and then further edit in Aperture?
I cn only show you Apple's tech specs with the requirements.
So if new Raw support in both Aperture and iPhoto requires Mavericks then that is a bummer.
The new raw support requires Mt. Lion, not necessarily Mavericks, says http://support.apple.com/kb/DL1706
But Aperture 3.4.5 is supposed to work with Lion.