Legally...If you already own them, then yes. If you are acquiring them for the first time, then no. Say for instance, I own some 20 round M14 mags and I travel out of state for a high power match. I can then legally bring them back into the state as they were my property before the law went into effect and so the grandfather clause kicks in.
Brycom1 is right though... only 2 counties have sheriff's that claim they will enforce the law (Denver & Boulder).... and even if they decide to enforce it, it is difficult for them to prove you didn't already have those magazines unless they are date/time stamped with a date that is after the date the law went into effect. The burden of proof is on the state in this case and unless they catch you in some sort of magazine buying/selling sting, that isn't an easy hurdle to overcome...which is why all the other sheriffs think this law is stupid and unenforceable.
Long story short, if you can find someone to ship you magazines that either aren't stamped with a date or that date is before the ban went into effect, nothing will probably come of it....but it's up to you to decide if you are willing to take that risk.