It’s actually not a good idea to let a female cockatiel have paper or cardboard to shred. This is a big hormone trigger and can cause her to start laying eggs. They do love shredding paper because shredding is a natural nesting behavior. Female cockatiels are known for becoming chronic egg layers in captivity, to the point that you have to take her to a Vet for a hormone shot or implant to get her to stop. It is very hard on her system to develop and lay eggs, so when a cockatiel lays clutch after clutch, she can eventually die from the strain on her system. It is generally recommended not to let female cockatiels shred paper items or have anything she can get inside of to use as a nest. I would recommend finding some fun toys for her to chew on instead. I don’t know of any places that sell paper rolls other than where you buy office supplies.
Thank you for asking Lafeber,