Benelli Super Nova Tac & 18 922(r) Challenge

[advocatusdiaboli]

In stock condition, the Benelli Super Nova Tach (SNT) is compliant, but I would like to add an extended mag and remain in compliance with 922(r). For example, since the stock M4 comes with 13 foreign parts, one has to replace 3 if one mods the gun. BATF is nice enough to give a parts list (total 13) that must be reduced to 10 foreign parts max for the M4. Therefore, in order to make the M4 compliant, you cannot just add an extender as your foreign parts count would be 13, three over the limit. So you need to replace the whole mag tube to keep the foreign parts under 11 by replacing 2 foreign parts with one US part (still need one more part but a simple stock change will suffice). No one provides such a list for the SNT but I assume the count will be similar though I'll probably have to ask Benelli to be sure (and I will since I want to be 100% compliant with certainty).

FYI, the ATF parts list is:

Receiver
Barrel
Bolt
Bolt carrier
Gas piston
Trigger housing
Trigger
Hammer
Disconnector
Buttstock (with integral pistol grip)
Forearm/handguard (forend)
Magazine body
Follower

Here's the rub: unfortunately, I cannot seem to find a solid mag tube for the SNT which would solve the problem handily (2 parts—still need a simple stock change or something else). Mesa make a nice stock called the Urbino. LGS don't have any parts or advice. Anything for the M2 *might* fit since the guns are very similar, but I doubt M4 parts will. Anyone have a source for a legal mag extension for the SNT or am I out of luck and need to learn to be happy with 5 rounds in the mag and six in the Mesa carrier.