GPL restrictions don't come into play until the point of redistribution. That is at least true for GPLv2, and I'm pretty sure for v3, but I don't know it at all.
In short, I can modify the GPL source of an application all I like if it's an "in-house tool", and I am not required to resubmit my changes. It's only if I attempt to sell it or redistribute the application in some way that I am required to.
That is not an IP violation.
You can't simulate scarcity with access provision. We've solved that. We wouldn't be having this same stupid tired runaround if access provision worked or could be made to work without being repugnant.
As for the Elvis singles, those were physical goods, housed in physical places, with physical companies. This is vastly different from people giving away byte patterns to one another--and the sooner this is accepted, the sooner we can all productively talk about it.
As for your GPL license...
I'm willing to wager that, shock, there are a lot of companies that use in-house tools having modified GPL source without publishing their changes. I'm willing to wager even more that in developing nations there are lots of IP violations of that nature occurring.
Your law means nothing if it cannot be enforced.