What kind of source would satisfy you?
There are laws about what happens to me if I break into your house and steal your property. I can therefore find you case precedent indicating that a TV is property because people have been charged with violating those laws when they steal a TV.
But I can't present to you the absence of such a thing. We have trademark, copyright, and patent law, but as far as I'm aware there's no crosstalk with things that talk about property, things like armed robbery.
> What kind of source would satisfy you
Any lawyer making this argument.
> I can't present to you the absence of such a thing
I’m asking why you’re saying data theft isn’t codified under U.S. law. (It isn’t comprehensively, at least at the federal level. But it’s surprising to claim it doesn’t exist at all.)