If I remember rightly you need to buy the Giant Carp Pack which includes Gillhams and Wraysbury venues plus these baits and size 2 hooks which you will need to use with these baits. Noting that if you don't have a size 2 hook selected on your rod setup then the dead baits wont show up in your inventory. Hope that helps...
The dead baits are a part of the core game. When you equip a size 2 hook they will be available in the list of baits.