Guide rods made for Glocks..... Lonewolf, GlockStore, Midway, Taran Tactical, RockyourGlock, Zev, Ranier, Brownells, Amazon,
If you are going down in spring weight, you can use the OEM. Crank the slide back, pop the tip off, put the new spring on the rod, rack it back, and stick the tip back in. This does not work for 20lb and higher spring weights as the plastic insert will not hold it in place. Even if you do not replace the tip, it's just un-captured.