There are tons of stencils out there if your goal is to mark your quilt with a marked line to follow while stitching. I don't know anyone who's done a Baptist fan with a walking foot, though. It's usually done with a darning foot as a continuous line (FMQ) design.
Here are some links to some stencils, though, in case they may be of some help to you. You may have have to make your own stencils, though, in order to get the fans large enough to do with a walking foot. You might try the Golden Threads papers. Or else I've made templates with a hot knife (avail at local craft store) and standard template plastic before. Just draw your lines & cut.
https://www.fulllinestencil.com/shop...7-baptist-fan/
https://www.connectingthreads.com/to...n__D82321.html
http://www.quiltbug.com/notions/quilt-stencils-3.htm
Here's one that's a single Baptist fan template, but larger:
https://www.amazon.com/Wrights-2-Inc...tpmotherhoo-20
Don't Call Me Betsy website claims it's big enough to do with a walking foot.