I use two different types of curve templates.
One, an exact router/trammel plotted centerline marker, suitable for drawing a C/L or running a router. These are not available.
The other type is an assortment of jig saw cut radii used in conjunction with tangent pieces to trouble shoot the actual fit of drawn plans.
Not a precision edge along which you would want to run a router or Sharpie, however they will help to visually approve your intentions.
At this point I have several dozen of these 8' long Masonite templates available gratis for a local pick up.