I make my own using vellum paper (kind of heavy tracing paper) rubbed with a soft graphite 5B or 6B pencil.
Works fine. Also...Before you do a new tracing make sure the paint is completely dry so it doesn't easily hold on to the tracing material.When tracing use as sharp a point as you can.
As you mask let the sharp traced line show a bit so you can paint over it...little erasing needed.
Tracing and masking precision take time but give clean professional results. If you are air brushing take 3 to 5 light coats to achieve complete coverage of any color. Patience = Good Paint.