Marty,
The rear grip is the first thing that is put on a rod during construction. It is pushed from the tip to the butt of the rod. It cannot be put on from the rear due to the taper of the blank. If you were able to get a rear grip to fit from butt to tip, the forward portion of the grip would be loose, and would never sit properly. I've rebuilt tons of rods, including saltwater rods. None of them have ever had grips that mount from the butt to tip.
Shakespeare does not have replacement grips for rods. It is not cost efficient for them to do so. A good aftermarket place to buy replacements is Mudhole Tackle or Custom Tackle Supply.
I also do not recommend drilling holes, and very much disagree with your idea of using a set screw to secure it in place. Drilling a hole into a graphite, fiberglass or composite blank is a sure fire way to ensure rod failure from that point. You would be creating a weak link in a rod.
Gorilla glue is also not something I would recommend putting a reel seat on with, particularly a salt water rod. There are products designed for the job. Yes - you could probably "get by" with it, but why? Use what was meant to be used for it. I highly recommend using Rod Bond By U-40.
Sorry Marty. I'm not trying to be disrespectful. But as someone who has built rods / repaired rods for a VERY long time, I have seen just about everything you can imagine, including your recommendations for the repair. In the end - they ended up on my workbench for repair. The "drilled and pinned" examples (I've seen two in my time repairing rods) were both splintered from the point of drill / pin, and the rod blank was unsafe to use again. In both cases, I showed it to the owners, and they agreed - throw the blank away because they had ruined it by drilling.
All the best,
Glenn