Here are several types and sizes, I actually drew these myself in Paint and then resized in Photoshop so they won't be exactly like the celeb's brows, but in my opinion they are close.  I drew them freehand in Paint so they will be off a little.   One set (General Stencils in various sizes) is modeled after one shape my friend sent me from a cheapo beauty store in NY. I changed it to be shorter though and less like a paisley. You can use a copier or Paintshop Pro to resize them if need be. BTW the red dot was only to allow my program to save it as a .gif.  It wouldn't save a monochromatic graphic as a .gif for some weird reason.

Making Stencils For Cosmetics
Resize them to find a size to fit your face. You can cut out the black part if you want FIRST and then determine which is the best size, then buy contact paper or other clear plastic and trace it.  Then change to any shape you desire. Then once you determine a shape you want, use an Exacto blade to remove the brow part from the plastic, leaving a stencil.

Making Stencils For Tattoo Transfer
Resize them to find a size to fit your face.  You can either draw on your brows like you want and then secure a piece of firm, clear plastic to your face so you can trace your brow shape onto the plastic or have someone else do it.  Then trace it to transfer paper. As is commonly used at tattoo shops everywhere. It is a bluish ink that has tracer paper on it and basically the design is traced onto this and then ink can be transferred to your skin.  This stuff can transfer any design you trace onto it to practically any surface.

Celebrity Collection 1

Celebrity Collection 2

General Stencil #1 (3 sets of the same size)

Various Sizes of the above stencils 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 (3 sets of the same size) Stencil 1(above) fits me best.  Print some sizes out for yourself, or resize them in Photoshop, and see if one of them fits you :)