Probably Metal Magic, in the Yakima area. I believe they supplied all the cut/bent/welded metal parts including frame elements.
However, its probably more expedient to take it to a local welding outfit. I'd try somewhere that does "trailer hitch" work in your area. this is pretty low tech stuff. while at it, might ask what they think should be done to alleviate the reason it wore through, as that's not supposed to happen. They can probably suggest a firmer solution so it doesn't happen again.
Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project