User blog comment:Chrismh/Coord Competition Round 3: The Idol Twins Debut!/@comment-3237624-20170503021649/@comment-29752621-20170503230345

It's on each of the coord's pages:

For example -

http://aikatsustars.wikia.com/wiki/Dreaming_Princess_Coord

Scroll down to the images of the coord pieces without the card, and then click the image you want, and it will have the file name for the image you want to attach