Ive used american rim supply barrels before and
http://www.amcrimhalves.com/Rim-Halves/ , they claim they get their supply from triangle hard alloys who are a supplier to hre.
This place offers stainless barrels which will give you a better shine and easier to maintain finish than aluminum but with added weight and cost
http://www.tunershop.com/Wheel_accessories/Outer_Lips