I don't know about glocks, but the S&W M&P have polymer frames with steel inserts, so even the frames still have metal in them.
There isn't a single individual part that a Glock can be broken down to that doesn't include metal.
Here is a complete Glock Model 17...the original complete with 17 rounds of 9mm goodness.
Here it is stripped down to its 5 major components for cleaning.
Here are the parts that are made out of steel (about half the dimensional proportions of the gun...and most of the weight aside from ammunition)
These are the plastic parts and every single one of them has metal in it. You couldn't even break this gun down and smuggle one part of it through a halfway decent security checkpoint. And even if you did get these parts through, you couldn't possibly use them without the steel parts and the ammunition.
Edit-I've put several thousand rounds through this gun. It is the most reliable gun I've ever owned. I bought it new in 1994 along with 2 spare magazines so I have 4 original Glock 17 round magazines.