I replaced my SD9 plastic guide rod and recoild spring. The metal rods are available for the SIGMA and are interchangeable. I got mine at Wolff Wolff Gunsprings - Firearm Springs for Semi-Auto Pistols, Revolvers, Rifles, & Shotguns Stock number 53618, S&W SIGMA Recoil guide & Std. Spring 18LB. for $29.95 and $6.65 shipping.
It made a lot of difference inmy gun.