Yup, I second iRunguns. Despite the exchange rate, the high shipping cost, etc., once all in, the PMAGs 5/30s are still a great deal compared to retail in Canada. I have bought lots from them. iRunguns also has a variety of Lancer mags, which I have found excellent in my 5.56/.223s.
A few of the sponsors have PMAG 5/30s and the prices are fairly competitive. FOC just got PMAG 5/40s in as well.
Tenda had a great sale on C Products Defense LAR15 metal mags for 5.56/.223 which were cheaper than anywhere else but I believe it is sold out now.