I need it around 580x800mm , I thought of getting a t-slot cutter and doing it myself but I'm not confident enough yet to try hehe.
even though my bed area is 690x1000mm but the spindle cant reach all that space, so the effective area is less, and also it would give me space from all around to insert nuts and so (if i go with the horizontal option)

did a quick search and found this company http://www.jashmetrology.com/product...s-base-plates/
they sent an email with a pdf to fill with all the details of what I require, but I'm pretty sure its going to be expensive