Actually, here's a bigger version of your avatar:
Just do what the other guy said, but in the URL you'll see some numbers at the end. Just go to those and type in something way bigger than the original number. For instance I typed in 900. It won't be that big, but it will be its fullest size. That way you get a bigger version of your avatar and can do whatever with.
Can't you just right click the avatar then click open image in new tab?
This is how it looks like: http://static-resource.np.community.playstation.net/avatar/3RD/JP00821101001_24FB25073906BF7BFFE4_L....
compared to this: http://assets.np.us.playstation.com/avatar/WWS_J/J0035.png?w=900
plus you can just removed the "?w=900" and it'll be the fullest size.