Here's one that Lotus makes- http://www.lotusviewcamera.at/subs/1...ssories_e.html. I think that's an 8x20 in the picture, so it might be overkill for a 4x10.
I made a knock off out of 80/20 parts for a 5x12. The 1"x2" aluminum extrusions (10 series) with the joining plates are plenty strong enough if you decide to build one. Very simple to make, the only tricky part was mortising a 3/8-16 thread hex-sided coupling nut into the extrusion for mounting on the tripod screw. The coupling nut is as long as the extrusion is thick, and is secured from above with a short 3/8-16 matching bolt and a lock washer.