Can't help much with the icing - just royal I guess. But if you search under the pattern area you should find quite a few tiara's. Doug may have one in his pics.
Good luck! 
Royal...I just did a few of these and they turned out great. The girls loved them! All I did is use one egg white and beat in sifted icing (powdered??) sugar until it was the right consistency.
I just made one the other day. I used a royal icing recipe from this site (meringue powder, powdered sugar and milk) and then followed the tutorial on the home page of this site. I also found a pattern in the gallery section under sketches. It turned out well, I did have one break in the crown, but it was really easy to repair.
I do mine out of gumpaste or fondant. There are a few in my gallery, but I just form them around an empty Ovaltine can. I'm happy to share more details if you like.
Have you also seen the tutorial (under articles) on this site? Someone did a step by step using RI. It looked amazing when they were done.
Here's the actualy link. It was done by carrielynnfields (who does AMAZING work).
http://www.cakecentral.com/article113-How-To-Make-A-Royal-Icing-Tiara.html
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