Originally Posted by NorthMtn
Thanx to everyone who gave input on my question.
I found exactly what I was looking for.
It's called the Glock Magazine Sleeve. It extends the grip size of the G30 to that of a G21. $12 each.
It's not the size of the dog in the fight.
It's the size of the fight in the dog!
I never did find that extension, but I think it might be the one Dizzll pointed out — the Scherer.
I'm glad you found what you're looking for. If it's what I'm thinking of, you'll need Glock 21 magazines. I believe the sleeve fills the gap between the baseplate of the longer mag and the bottom of the grip.