This off-the-shelf extrusion was posted several months back: MisumiUSAExtrusion
This is available in a 250mm width and can be ordered at a desired length. The post had pics of an XXL with this full aluminum bed extrusion. The downside from the poster said that it wasn’t as rigid as he would have liked.
I could go investigate options from some local shops, but I believe there would strength in numbers. I’d want to acquire it before moving as well, so I’m hoping there’s something that comes from continued discussion. This is not the right thread for the discussion, however.