I assume you mean "dual wielding" in sense that it's against a single target?
Assuming true, I guess that answers my question. There is no rule, and further it's not intended to be allowed, despite how illogical that is.
Realistically, if i can look left, and go "pew pew" with one gun, and then look right and go "pew pew" with the the other, then I have the time to simply look straight ahead and go " pew pew + pew pew". I think I've posted my own fix to that, at least with guns. Treat as Narrow Burst. Two BF attacks would be -6AR for a +3 to damage or something.
I get that you don't want to allow two separate baseline DV occurrences against the same target with the same action. That math is lousy.
However, per the thrown weapons rule, those weapons get to do exactly that.
Boosting AR for dual wielding melee weapons seems reasonable, tho not very satisfying. Also runs afoul of the off hand penalty. If its a single roll, should it get Edge or not? Etc, etc. Melee definitely gets trickier.