I found a small silver "Aikido" necklace charm off of Ebay several years ago. You might want to check there every now and then.
I also have an Italian charm bracelet "Aikido" link from
http://www.italiancharms.com. Either look under Martial Arts under the "buy loose links" option or just do a search for "Aikido". They will also let you create your own and I created another charm with my Aikido school's name lasered on it. It's awesome and very special to me.
Robyn