Off top of my head:
AndyMark Sells this:
http://www.andymark.com/product-p/am-2622.htm
They also sell this, which might replace your entire thing depending on what you're doing:
http://www.andymark.com/RAW-Box-p/am-2372.htm
VexPro sells Bevel Gears alone (
http://www.vexrobotics.com/vexpro/mo.../217-3344.html
), if you can create a bracket to assemble them that mates to the VersaPlanetary. Not sure what your machining capabilities are, but I know I could make such a thing with some 1/4" aluminum, drillbits, taps, and a drill press, or just sheetmetal capabilities.