carlabs x-brace did, but its heavyish and $$$. I think TIC bought the rights and is doing it now. $450 or so.
Then there's the Litespeed Chassis Bridge. It's essentially two cables, diagonally across the trunk opening (where rear seat-backs would be) exactly the same place as the X-brace. It, too, prevents parallelogram-ing. But it's along the linkes of $150.
Then theres the Home Depot Racing (HDR) version of the Litespeed Chassis Bridge. It's EXACTLY the same, except its DIY. I bought way too much stuff (to avoid having to drive back to the store) and did it for $15 IIRC.
To those skeptics, It works.
Here's the rigid/welded X-brace, unbolted at the bottom:
And my annecdotal evidence is from backing into my old parking space required backing over a drainage ditch where the car wanted to tripod which led to a lot of squeaking. After installing my HDR chassis bridge, the sqeaking almost disappeared.