Gantry bearing mounting extrusion

[threedee]

Planning on reworking my laser cutter.
Trying to figure out how to increase Y rigidity, essentially requiring full rework.
Need to put down reinforced thicker rod, at present measly 12mm for 750mm of length.
Way too flexy.
Machine travel is about 600mm.

This aluminium extrusion capturing bearing and carrying gantry, i cant figure it out where do i get something like this for bigger, and maybe open, bearing (16mm? 20mm?). What is it and where i can get some.

Alternatively, any ideas on how to proceed ?