Trailready and copperhead among other.
If you have the wheels and the welding skills to do it yourself "safely & correctly" it will cost you about the same as the spacers, actually less (press in or flat) if you have to buy or ship then the wheels and or have some one do it for you, it will cost considerably more, with out options.
By the way, I have used aluminum spacer on my M1008 since April of 2005, now about 35K. miles with out any problems, other then their heavy weight for a 36" tire/wheels/incerts let alone the heavier 37".
Buy good ones, 4 1/2" bored for Chevy's or 4 3/4" for some ohers, SAE lugs or 14 m/m, follow bolting pattern, torque to specs and re-torque then twice the first couple hundred miles (Aluminum has a crush value) and every time you rotate the tires and they will be as trouble free as anything man made. I will not say that it has not happened, but I have not heard of any failures either.