Click here to downlod the theme card PDF Print. These are all standard MTG card sizes, so you can print, cut them out and put them into your packs.
I would recommend printing them at a local print shop or somewhere like Staples (you can select cardstock for more durable prints) and slide them into a sleeve to serve as the traditional Jumpstart Theme Cards.
If you’re interested in creating your own packs, MTG Cardsmith is a great site where you can create custom Magic cards with your own text. Unlike traditional Jumpstart theme cards, with MTG cardsmith you can add information as well as flavor text.
Additionally you can create your own more traditional theme cards and lists to insert in the packs at Burger Tokens using their Jumpstart custom Theme Card Builder.