Supporting a glass floor panel as a part of a floating deck
You can get angle iron at your local home improvement store. You would probably want to get some strip foam for padding. This can be as simple as strip closed cell foam for weather stripping around door frames, or it can be more of a rubberized material for better wear and less likely to compress. This can also be weather stripping for doors.

I'd go with at least 1" steel angle, which will deflect much less than 1/2". If you really want support, go for 1-1/2" steel angle or 1" steel square tube. The larger angle might not be as readily available, but the square tube can probably still be sourced at home improvement stores. I know Lowe's, Menards, Ace Hardware, and Home Depot generally carry the 1" angle and the 1" square tube.

It's mild steel, so paint it or it's likely to rust. Even though it's "mild" steel, it should still provide plenty of support for the glass.  Seeing as the glass shouldn't deflect at less than 600 lbs. anyway, this is more for looks and your own piece of mind, rather than structure.

Also, I'd support it from the deck, not the house. Even though the deck is attached, there can still be some movement between the two. You don't want the glass panel to become a tripping hazard when/if the deck sinks even 1/4". I'd also use lag bolts. In my experience nails have a tendency to work their way out. Deck screws might be enough, but they also might not be. With lag bolts, one on each end should be more than enough and aren't likely to ever come out.