I bought my watch face at a local craft store (Porters) but you can find them at craft stores in the beads section…or here, here, or here online. Mine was about $10.
If you want to make these for gifts but don’t know how big the recipients wrist is, make them a tad bigger and either use a larger strip of velcro, or a couple of D rings so it can be adjustable. I would make the strip larger and add 2 or 3 sets of snaps so that they can make it tighter or looser. I’m pretty sure every one of my friends/family is getting one of these for Christmas.