Contact Heartland Customer Service (877-262-8032). They can give you the contact info for a 3rd party that we sell our older graphics too. That said, current graphics are generally kept in stock by Heartland for some period of time.
As I understand it, the ability of the decal to be released from the backing paper decreases over time. As such, rather than tossing only graphics, Heartland sells them to a 3rd party and they stock and resell them. So if you can find out who has these - buyer beware on them I guess. They may release well, they may not. Ask the seller about it and about any refund/warranty on what they sell.