IT'S A MAGAZINE geez of course u can
According to Gunparts Corp in the US, magazines in excess of 10 rounds are ITAR, other mags of less capacity have no military value UNLESS for 50 BMG. Like I said I have ordered 12 three, four and five round mags in the last four months. No problems.
Gunparts Corp/Numrich is a licensed exporter, so your scenario does not match the OPs situations of an individual-to-individual sale. Do you have a reference to the exemption of < 10 rd magazines from ITAR? I've never heard of this, and am skeptical, but would love to be proven wrong.
I've a friend on an American forum wondering about the legalities of shipping a BLR mag to Canada?