Make them yourself.
You will need a good knife, extra blades for the knife. Maybe a printer, and some thing to make the stencil out of.
You can just use paper, its fine for a quick one off stencil, but certainly will not go through more than a few uses maximum.
I've had success using acetate sheets, you can get printable ones too, but theyre clear... so you could lay one over a print out if your interested in tracing a printed design for ease.
To make them tacky (if you desire them to be) for sticking down to the target area temporarily. You want to use somethign called 'repositional spray adhesive' 3M make one, a few other brands do too, but more often than not you will find permanent spray glue... this is not what we want.
Also patience... cutting a stencil by hand, especially at our tiny scale, is a fine art. Do one good one... thats all you need

so take your time with cutting. You could invest in a fancy cutting machine too

but that might get steep quickly.
Alternatively seek premade ones such as the ones linked above.