The only aftermarket I've ever seen for Envoys are these type
02 08 GMC Envoy Tail Lights Rear Brake Lamps Black Blk Assembly LH RH Pair New | eBay
Personally I think they look horrible. The stock lights don't exactly look good, but sprayed with either VHT red for all red, VHT Niteshade for tinted, or swapping to Ascenders looks way better to me.
Dmann I say you tint them, but removing it isn't easy like Plastidip. It's regular paint, so you need to use thinner to remove it. I would honestly spend the extra money to take them to a body shop to have sprayed the correct way. Tinted clear as a base coat, and covered with clear afterwards. Sanded and buffed, it will look like a mirror. Nite shade I noticed had a brown tinge to it in direct sun light, and it also has red inside so it made my orange turn signals look red. Overall it looked significantly better when sprayed with true automotive paint out of a gun.