No factory-made metal rods for the Gen3 and earlier full-size and mid-size (G19) models; the sub-compacts and the Gen4 full- and mid-size guns come with the two-piece double-spring recoil spring assembly, which is metal, but it cannot be used in the older guns.
Sometimes, aftermarket metal guide rods and different-weight springs can be a source of functioning problems. Several times I've had folks come to me to get a functioning problem with their Glock diagnosed, and pulling out the aftermarket metal rod and replacing it with the factory recoil spring assembly (RSA) was all it took to get back to 100% reliability. Usually, it was because they were running a heavier or lighter spring than needed, but at least once it was supposedly the same weight as the factory spring.
I've never seen or used an aftermarket RSA for the sub-compacts (G26, etc.), as the original is metal and I don't think any aftermarket company has been able to significantly improve any aspect of the performance of the original part. If they claim otherwise, I'd want to shoot a modified and unmodified gun side-by-side to actually feel the difference. Not saying it couldn't be done, but even if it was, the VAST majority of normal shooters probably couldn't detect or take advantage of any tiny improvement. In those cases, the money is probably better spent on professional training or practice ammo.
I currently have a double-handful of Glocks, have been shooting various Glocks for 20+ years now, and I've never had a problem with a factory rod/spring assembly. Metal rods and different-weight springs are a solution in search of a problem, IMO. They MAY be useful for dedicated competition shooters trying to reduce recoil with light springs and mouse-fart reloads, but otherwise, I recommend avoiding them.
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)