They are usually custom made. Find yourself a metal fabricating shop, tell them what you want and see what they can do for you. Or, buy some metal, a welder and a few other toys and try to build one up yourself. It is a fun task. I plan to build one up some day when I find a decent canidate for a pure brush chopping tractor. I want to design it in 3 pieces. A front section, top section and rear section all bolted together so I can remove it easily if need be.