Airbrushing stencils are pretty easy to be making
For a single use paper can work fine, but for something to be used again and again you might want something plastic or glossy with a bit of strength to it.
I've not heard of 'contact paper' before, but it sounds like a branded product I know of called 'frisket film'. Which reminded me of sticky back plastic that we covered school books with

Only much less sticky, it only had a mild tack to it so it could be pulled up and or re positioned easily.
If you happen to know anyone with a plotter (Wouldn't be suprised if you do not) they might be able to help you machine cut complex shapes with precision for your stencils. I've got a (relatively) cheap home craft grade of plotter which has seen some great usage making stencils for use on canvas, but It would struggle at the scale of say a shoulder pad design, but might cope with vehicle panels perhaps.