I want a solid guide rod

The rail fit slide to frame is what controls travel, spring tension powers the second half of the cycle to chamber the next round. About all the rod does is guide the spring to keep it controlled. A hollow rod or even polymer is evidence there isn't a lot of stress on it. Solid rods are traditional mostly because it's cheap to hack off a length of inexpensive round stock to fabricate it - old school gun fabrication on an assembly line. As the price of finished steel went up, new methods and materials were sought out. Some pistol designs even put the spring around the barrel - but it was subject to a lot of heat by overenthusiastic shooters.

Solid rods are used by competitive shooters to add some weight to a gun, when lasers first came out, they were built into guide rods complete with battery. Those work pretty well and are still available for each specific firearm. Eliminates a new holster, too.