A few years ago, I purchased RV-6A and RV-8 shadow art placards sold by Wicks. I cannot find the items in recent catalogs. I did however use an Internet archive service and through it managed to locate the items. Ideal for clip art, you might want to copy and/or modify the images to suit. Here is the archive link to a Wicks catalog of a few years ago:
New information: While conducting an unrelated search, today I discovered a source for clip art, lots and lots of clip art. I remembered this thread and updated my post by adding the link:
