I recommend this pattern. It's easy, repetitive, and it makes a thick, full flower. I tied the rose on to the ear warmer headband, but it is definitely removable.
My friend sent me the link to the pattern (I loved her roses she was making for her own headbands!). You can find her Facebook page with her crocheted items here: Blessings by Charity.
The ear warmer headband pattern: here.
The full rose pattern: here.
Both of these items will be available at the craft show (together or separately).