I'm not quite sure what you're asking exactly.
The gimmicked deck is "Unshuffled"
So, using your words, to '...buy a deck of split cards as extras...', you'd need to purchase the trick again.
I've never seen a complete set of longitudinally split cards other than "Unshuffled".
However, since PM doesn't have them available, check out this site.
http://www.mimesis-magic.com/gaff-cards.html
Shawn at Mimesis makes the best gaffs available, bar none. Gimmicked decks also
Check it out.
Hopefully, PM editors don't delete this ;-)
Good luck!