Often the manufacturer of the panel will have free patterns available on their website. You can also google images of panel quilts or look on Pinterest. I have made a couple of quilts out of panels and also quilted them for other people. Here is a pic of one I made:
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Here is a link to one I quilted but did not make. This one is a free pattern offered by the manufacturer.
"Peony Fantasy" an Asian Panel quilt massively quilted