Not sure if this has been suggested before but obviously I think it should be quite rare. Possibly a rare item you can get for your birthday or anniversary? Maybe an extreamly rare hunting find? Like reeeeally rare.

I feel like something like this shouldnt be something that you can buy with currency but randomly get, but Im happy to see suggestions.

Elephant Afterbirth
This rare nutritious delicacy will guarantees at least 4 cubs in next breeding. Eaten by female.