I think Kawauchi's book has tables that include ribbon diagrams, but I don't have a copy with me. Look at 
<a href="http://www.indiana.edu/~knotinfo/diagrams/8_20.png"> Livingston and Cha </a>. It is not hard to get a ribbon disk from this diagram: add a handle between the ears on the top and bottom right. 

Generally, I check <a href="http://www.indiana.edu/~knotinfo/"> Livingston/Cha </a>, <a href="http://www.math.toronto.edu/~drorbn/KAtlas/Knots/8.20.html"> Bar-Natan, </a> and <a href="http://shell.cas.usf.edu/quandle/Invariants/database/database.php"> Saito </a> for various information.