Honestly, I am surprised that General Kalashnikov did not purposefully put in a bolt-hold open mechanism into an AK or its magazines. Recognizing the potential advantages of the system, the Yugoslavians built the functionality into their magazine. Sadly, Yugo magazines are expensive (I consider $25 expensive for an AK magazine) and can be harder to find.
Jerking the Trigger posted up a source for new Croatian magazines which are currently available for $10.95. The Magazines are in VCI (not cosmoline) to prohibit rust. The Croatian magazines are a direct copy of the Yugo design.
For those looking to modify their own. MrGunsnGear has a good video on the functionality of the magazines and the required modifications (Note- He uses Yugos, but they are functionally identical).