Discount Trailer Warehouse in Hollywood has them, but they're not cheap. The metal brackets are about $40 a side (ouch)

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If you're handy, you could problably make some out of 2" PVC pipe & fittings, and some SS or galvanized u-bolts.
IMO, this is one project is well worth the effort. Make sure that you use heat-shrink on your wire connections, and solder them if you can. Yea, it takes longer, but it'll last a lot longer too.
Good luck!
DD