As to not using them yet, the wahabis who control the terrorists are still milking the US for hundreds of billions of dollars, they have no wish to kill the goose that laid the golden egg, nor do they wish to use them on israel. Nope, they are waiting for china to get strong enough so they can switch public allegiances, then they might use them.
Finding loose nukes with radiation counters, etc. I'm not sure, but I don't think they repealed the use of lead sheets yet. Only one in 200 containers is opened and inspected coming into the US, and a WHOLE lot of them are carefully not opened due to large sums of money changine hands.
I wouldn't worry as much about the used russky nukes, as worry about the brand new chinese ones that are probably here and will keep coming in, now those babies will work, and have a big bang.
Fair warning advice to anyone,any major urban area="target zone", do ya feel lucky?
If the devices were old and in need of a tritium recharge, a Russian in need of some cash would be tempted to sell them to the OBL operatives, "knowing" that the devices were duds and could not be used. It is possible even that the OBL operatives did not identify themselves as such, but rather claimed to be Pakistani agents, trying to scrounge up as much fissile material that they could to recycle into their own bomb program. The Russian might have figured that the Pakistanis already had the bomb anyway, and that by helping them to even up the balance with the Indians he might actually be doing the world a favor.
What he wouldn't have known is that OBL operatives (again possibly claiming to be Pakistani agents) would also be talking to other cash-strapped Russians about purchasing a fresh supply of tritium.