SRAM file is not the same as FROM file(NC Basic). SRAM file stores your parameter settings, PMC settings, programs etc. NC Basic is the operating system software for 18MC control.
If you are looking for FROM file NC-Basic, you need to know what series software you originally have on this control (such as BDxx). Please refer to Fanuc datasheet that comes with your machine. On the other hand it is almost impossible to get SRAM file for your particular machine since parameters are unique to your machine (unless someone has an identical machine with same control and can do SRAM backup for you).