Just got around to doing this my self. My front seats were in bad shape and needed a complete going over. Most of the thin springs were missing as someone had redone the interior years before I got the car. It was velour and was a nice job at one time, not much care was given to originality. What I did was to buy some straight spring wire 13" long .040 dia. and some burlap from McMaster-Carr. They have a very nice web site for all kind of things hardware. The springs are spaced at 1 1/4" so you will need 14 for the 18" long pannel for the bottom of the front bucket seat. I then cut the burlap 15" wide by 20" long and folded it into pleats(like and acordian) 1 1/2" wide along the 20" length. Then stick the springs through the burlap and unfold. You then have a 1" border to fold over and glue with spray trim adhesive or if you have access to a sewing machine you can sew the sides or you could use duck tape. Anyway you get the idea. Good luck..
Sam