Looking for a certain battery disconnect switch

No idea. I would get yourself to an actual truck shop. AKA one that works on big rigs. Be sure that you want one. Will it discharge the computer memory?

And yes, I have an 01 with two factory batteries. One hot cable from battery no. 2 jumps across to the main battery, and then right down to the starter

If you are concerned about amperage, you could split them. Put in two switches, one in each ground cable.