Another source for free designs is a child's coloring book. They usually offer simple, basic outlines with dark borders. You may have trouble finding the designs small enough, but this can be accomplished using a copier that reduces images.
When tracing, remember not to infringe upon the copyrights of another artist. You should transform the picture into something that shows your own style and talent. You could add or take away something or change the coloring, angle, or shape.
If you have a friend who works with patterns, such as sewing or embroidery, you could ask to borrow these to transfer the pictures to your own collection of free face painting designs.
Does your computer have a graphics program? Print some designs from that. Choose a blank document setting, add a graphic or several, enlarge or reduce as needed, then print in black and white. You'll want to transfer these into your notebook or onto a piece of poster board to showcase your available artwork, adding the actual colors of the paints you'll be using to give the proper image for public viewing. This will help you avoid someone wanting colors you don't have available, and will give a more realistic sample of your work.
Do you own cookie cutters with empty centers or know a mom or someone else who likes to bake? Borrow their cookie cutters to trace the outlines. Add your details and you have free face painting designs! Use stencils to trace designs for transforming.
Checking out books at the library is one way to come up with ideas for face painting designs. Ask your friends and family for unwanted craft magazines. Check with teachers and neighbors, parenting groups in your area, community centers, preschools. Don't forget the wonderful world of the internet. If you don't have your own computer, check with your local library. Even smaller towns are becoming more technology-friendly. Libraries now tend to offer free internet service to those who aren't able to have it at home.
Of course, once you have practiced and built up your collection of available designs, you may want to offer some free face painting to some of these wonderful people who have assisted you in getting started with this new adventure. It will serve a purpose for several reasons, returning a favor and getting your work and name out there so people will become familiar with you and your talent. Plus, it will allow you to find your voice for the public, providing practice on dealing with your customers and where to set limits for them and for yourself. You'll need to learn how much of your supplies to keep on stock for the size crowd you're expected to draw, how best to set up your area, and so forth.