30x30mm T-Slot Aluminuim Extrutions

#1
Hi Guys
Please could you help.
I am in the process of trying to build a Gmax printer & I only can get 30mmx30mm Aluminium Extrusions which I have now. Does anyone have the Raw / Cad files as I am unable to modify the STL files. I need to adjust a couple of the STL files so I can fit the 30x30mm.

I would appreciate your help

Thanks
Vaughan