I bought my 59 GMC back in 1989 and I have found very few trucks with a GMC grill and signal lights in them. I would think you could track down a grill as many have been replaced with Chevrolet ones, but expect to pay really big bucks if you want GMC signal lights in that grill! I saw an NOS set sell on eBay for $1350......
But there sure are pretty.......