I do not know of any way to make it so that the radios are on when I first load the C-130 into FSX/FSX-SE.
I find that the easiest way to turn the radios on, is to click on hotspot on the VC radio panel (upper aisle consol), which opens the 2D Radio Panel, then click on the the on/off knobs to turn them on. I find it much faster to do it that way, than to press SHIFT+2 to open the Simicons Panel, then click on the Radio button to open the 2D Radio Panel, and then turn the radios on, especially since the Simicons panel will disappear if I change my view (i.e. move to the First Officer view, or the exterior view).