Twitter user @kotori_ryo has posted images of a particularly impressive take on Grimlock as seen in IDW's comics - most recently in More Than Meets The Eye: Revolution. Using Transformers Adventure TAV30 Battle Grimlock as its base, which was itself a remold of the more G1-like Generations Fall of Cybertron Voyager Grimlock, the figure is a pretty good match for the comic version and has a beautiful silver and gold finish. Keep reading to see!
In the accompanying tweet, @kotori_ryo explained that the finish is a combination of two paints in the Mr. Color range of Japanese model paints: the base color is White Silver, while the gold parts were accomplished with a coat of clear yellow on top of that.
The tweet doesn't specify this, but the antennae are clearly from Mobile Suit Gundam model kits; they're commander's antennae for Principality of Zeon Mobile Suits.
TAV30 Battle Grimlock was released by Hasbro in an Entertainment Earth exclusive 2-pack with what was probably your sixtieth copy of RID Warrior Class Bumblebee. They have gotten some mileage out of that mold.