You can save back to older AI formats even in CS6 and things like copy&paste should work. Of course there may be a few caveats due to dat conversion. Otehrwise there's no way to buy legacy versions other than used copies with all the risks and extras like possibly ending up with fraudulent software and having to run a Transfer of Adobe product license.
Thanks, I'll keep that in mind...actually, I've been thinking about going with Corel Draw X6. I'm still up in the air.