is there someone or a company that sells all the printable platic parts?

The size of the three openings doesn't appear to be critical.

The control panel covers the edges of its hole and so doesn't need to be perfect.

The slots for the X and Z should still work fine if they aren't perfectly straight and square as long as the hole is wide enough for the arm to pass through and stops short of the rod mountings at either end. It wouldn't be hard to add some edge covers for these as well to hide any imperfections.

There also looks to be space to use nuts instead of threaded holes but tapping holes isn't hard and can be done using cheap hand tools.

The welding could be replaced by cutting a couple of brackets to bolt the corners.

The plastic parts on the blue prints should be the exact size to my STL files. Just had to re do it to make it STL compatible.

Printing foot with 20% honeycomb infill and still pulls from juiced mirror. so really stick it.