If you have an old retractable tape measure laying around, you can make some handy flexible scribing guides for your models. Just open the tape measure and take out the coil of spring steel used to wind the tape back in. You can cut this coil into different lengths with sheet metal shears. The material is strong but will bend pretty well around curves. Warning: The ends will be sharp after cutting! Be sure and file the ends before using. I cut the edges at a 45 degree angle on mine but I wish now I had kept the ends square.
Hope this is helpful to you,
Russ Feldt