K&K used to have the patch panels you're asking about. I myself purchased one (about 5" wide) from them a few years ago. From what I understand, they sometimes de-list the item until they have enough demand. They basically use the same stamping die as the big rear quarters, but instead place a smaller piece of metal where the patch is desired. The stamping cost ends up being the same as a full quarter, but with a lot less metal (and potential for error) involved.
You might want to actually talk to Tim Kidder of K&K for an answer to if and when they plan to re-stock these.