WordPress doesn’t store a copy of themes.
I see several options:
- Find out why the creator of the theme doesn’t have a copy of the theme at version 2.9. It is really weird that any serious developer wouldn’t keep a copy of old versions.
- Check your own backups.
- Ask your hosting provider if he has backups.
- How did you get the theme in the first place? Maybe you still have a copy in your Downloads folder or Mail Inbox?