Touchy issue.
I come from a country with no gun rights, at least not for civilians.
A spare magazine is not a restricted article. Anyone can buy or make. If the matter is 10 rounds, well, you can have as many mags as you want.
Or, have a big mag with fillers in it for inspection. When you step outside the police or whatever office, you just take those fillers out.
That's not "a little."