"There is no need to be so naive S-2, and turn this nasty."
Neither is the case. There is no ignoring Afghanistan's dysfunctional state. Neither, though, should I ignore similar conditions elsewhere. Unlike Afghanistan, though, Pakistan has a major port.
Weapons acquisition will come from any and every source possible and to whom these weapons go depends upon the organization. Ali Baba and his forty thieves will take, steal, murder, and buy from whomever.
Jalaluddin and Sirajuddin Haqqani have a massive and old network that might have more extensive supply requirements. So too Gulbuddin Hekmatyar. Both operate extensively along your FATA border. It makes little sense to suspect these men depend upon irregular supplies that will travel to them via the local ANA or ANP post. Equally, however accessible Russian arms are in Tajikstan, to suggest that they are purchased there, brought into Afghanistan and then transported through your eastern borders in scale capable of meeting and sustaining the arms needs of just these two prominent irhabists doesn't match the road networks nor the security risks when other options might be available.
This, of course, doesn't even suggest that the ISI has retained links to certain elements deemed indispensible to their long-term objectives.
"...bribing a gang of custom officials to ignore a container or two is not the same as channeling weapons sustaining a large scale insurgency that’s been raging for the better part of a decade"
That's EXACTLY how it's done. You play on an official's greed and he is TURNED. The more greed, the more TURNED. Once TURNED, there's no going back as you've a chance to be killed by either side, arrested, job loss, etc. Once in, there's no going back.
To suggest a gang of customs officials have been turned is all you need to extrapolate the implications for each. They'll henceforth roll every damn time. They've little choice.
I'm not off nor am I nasty. It's the toughest job in the world to handle port or border customs. We are CONSTANTLY looking for exactly the same criminal leverage amidst our own officials along the Mexican border or our ports. Drugs don't reach America entirely by virtue of Mexican "mules" in 1978 Plymouths driving north.
Neither do weapons in Pakistan. Not on any economy of scale necessary to fuel two insurgencies. I've no proof. None. No article. Nada so I won't follow-up with my speculation but I hardly believe it to be naive or uninformed and is certainly worthy of serious consideration if truly interested in determining where weapons arrive from and to where they are ultimately destined.