My fans are similar to Leia's and for those, I used 5/8" ribbon and wrapped them really tightly and had the ribbon overlap a bit. For each fan, I measured about 36 inches. I bought some of my ribbon at Michael's but it was pretty pricey, even though the ribbon was on sale. It was about $2 per spool. I ended buying more ribbon here: BBCrafts - Premier quality Ribbon, Pouch, Tulle, Satin Cord and Wedding Related Products Supplier
It was much, much cheaper - I got a HUGE spool of 5/8" satin ribbon for about $9 and it shipped quick.