It is very rare but I think you can get it by doing the following:
In the catalogue for the costume trunk, go to the viking section where there is a girl penguin wearing a viking helmet. Click the helmet on the word 'viking'. Get the red helmet. Press the 'x', click the same helmet again, close it, click the helmet again, close it then click it again but don't press the 'x'. This time press the helmet on the girl penguin's head.