IIRC, the grill is plastic rivited in, but they can be easily drilled out. Don't buy a new grill, just use the one that you have.
As for sourcing the new bumper, take a look at your local junk yards. I went to a Pick Your Part a few weeks ago to get some Caliber parts, they had two Caliber's in the yard and both bumpers looked like they were in good condition.