Is the plastic portion of the grip a standard AR unit? In other words, could I get one of these, and then put a green grip on to the metal rail grabber/throw lever part? From the pictures it looks like the grip is canted forward; I don't mind cutting away some plastic to get it to fit, if the basic part is the same. Thanks!

The new model QD pistol grips use the standard grip on that the weapon uses for logistical reasons. That slope forwad is built into the mount so that it better fits the hand in the extended position, so you will not have to cut anything.
Good Shootin, Jack

Actually, the grip will require extensive modification.  I'd post pics if it were easier, but I'll try to explain.  The grip is cut at a 30 degree downward angle from the top rear edge, and notches are cut into both sides of the top to accomodate the throw lever assembly.  That said, with a little careful cutting, it should be possible to fit a new grip to the throw lever plate.  If you don't want to do it yourself, give ARMS a shout, they're great people to deal with.

So how about us folks with the old one? How do get a replacement.