I don't know how much I can help you out because I don't care much for shot guns. Try Crappy Tire, Army Navy Surplus on Agricola St (Its between the base and the bridge, I think thats the right street - but definitly the one on the hfx side cause I don't think the Dartmouth side carries ammo) and you can try JD's out in Prospect Bay. Here's his address and #:
J D'S Shooting & Fishing Supplies Limited
45 Prospect Bay Road,
Prospect Bay, NS B3T1Z4
(902) 852-2551
(902) 852-2551 (fax)
Oh BTW: Welcome to HFX!!!!