Does anyone know a good way to get an autograph from Troy Polamalu?

I have a copy of Sports Illustrated from November 14, 2005 with Polamalu on the cover. My parents gave it to me a few years back. I'd really like to get Polamalu's autograph on it and have it framed so I can gift it to them as a surprise sometime.

I don't mind paying for it, shipping it, etc., but I want to make sure it's authentic.

Ironically at the top left it says "A star is reborn - Notre Dame quarterback Brady Quinn" and it just made me chuckle a little bit.

Anyone have any suggestions?