Googled and found
http://www.avatarist.com
Be careful as most free stuff is not really free.
Otherwise if you have a pic you would like to use you can resize it at
www.dynamicdrive.com or if you have some image editor resize it to 150 x 150 (if not square, leave off one of the sizes) must be 30kb or smaller.
if you google and then select search images you will be surprised at what you can get - careful what words you use.
Blessings
Blessings