The CZ24 mags have triangular cross section. They are not a square box. The triangular cross section directs the rounds from either side towards the chamber. They feed from both sides at the top of the mag. Kind of like a Soumi mag in 9mm. Like the 9mm round, the mag could be curved to spread the spring force across more of the body of each round and improve reliability. The soumi straight mags in 9mm and the CZ24 mags work great with the straight profile. The guns were eclipsed by the AK47 and AR15 developments.
AK-47 user and abuser since 1980.
How about building your own magazines? You could use tokarev magazines for the top section with the feed lips and just add metal to make it longer. The only downside besides having to make your own magazines is that they would only be single stack