With a son who takes TaeKwonDo, I am also interested in this subject. So, I did a quick search and found this site. Both quilts displayed here are very good options for TaeKwonDo quilt, I think anyway.
http://dellajanehanddyes.blogspot.co...or-alyssa.html
Another thought would be to do applique of a silhouette of a person doing a kick on a block. Would be fun to do one of the person you are making the quilt for instead of a general one found on the internet. The background could be the different colors of belts that they have achieved and some how include the date of achievement in the block or in the quilting of this block.
Hope this helps you out.