I browsed Ravelry and just couldn't find a pattern that was right so I just decided to make one up. It has turned out really nicely and Razza loves it, she has had it on since she unwrapped it yesterday, even in the cinema.
Should you wish to recreate one for yourself then here is what I did.
4.5mm straight needles.
Aran weight yarn (I used town end alpaca and the ball was 82m, I have some left)
Cast on 20 stitches using the long tail cast on method.
First row: k1, p1, k1, p1, p3, k6, p3, k1, p1, k1, p1
Second row: k1, p1, k1, p1, k3, p6, k3, k1, p1, k1, p1
Third row: k1, p1, k1, p1, p3, c6 to the front, p3, k1, p1, k1, p1
Continue in this fashion cabling on every 6th row until the headband is the desired length.
Cast off and sew the ends together using matress stitch.
If you have any questions then please don't hesitate to get in touch.