Its part of the bumper. You can remove it.... with a Dremel tool. The only replacement grill that i know of is made my Grillcraft. But it uses that lower grill part to affix the grill so dont remove it to quick.
I have seen of some cutting it out and putting their own grill behind it. I wouldnt do that unless its with powdercoated mesh. Otherwise its just not going to last. Better off to save up and buy the Grillcraft one.