I have what was an upgraded shapeoko2 to x carve that is 750 x 1000.
Inventables used to sell longer makerslide, but they haven’t for years. Openbuilds sells extrusion and bolt on vee rail called openrail and that might do the trick.
OpenRail® Linear Rail - OpenBuilds Part Store
Some here have tried butting up two pieces of makerslide, but haven’t reported back. Most people would reset the material and do a two step operation.
There are aftermarket risers, stiffeners, z axes, and 9mm belts and pulleys. They used to be sold by CNC4newbies.com and FAQ — tbd cnc, LLC TBD is now part of the Inventables family I believe. I bought all the upgrades and they are worth it.
X-Carve Upgrades | Inventables
For a wasteboard, I used plywood with 1/4-20 threaded inserts but they were too far apart and made clamping a pain. I ended up installing extra extrusion and using Tslot from Woodcraft. I posted it here a couple of weeks ago. I put basswood in between the t slot as it is a stable wood.
Here is a link