Through lots of viewing on here , there was one thread(Search beowulf if you want) I have read different companies come forward about being denied, one had the manufacturing completely set up for the beowulf mags and were denied when they sent in the mag they had made, sorry bud, I cannot remember the name of it, but I know they were denied. As far as the AIA 10 shot mags, I believe two distributors (Sponsors on this site) Were denied, they can chime in if what I say is true, if you believe me or not , that is irrelevant to me.
But what you are really asking is: "Why are they being denied the right to produce a CONTROLLED product" It's not just "Legal" You are not allowed to just whip up some mags cuz you want to, when its firearm related (For that matter, any controlled product) The government has to be involved and give it an OK. And when its magazines like this, they KNOW what they are for and why people want them.
But no I did not save any of the threads, so your just going to have to search it, take my word for it, or don't. Bottom line is , IF you are lucky enough to find them , they will be so expensive that the guns prices on EE will look like a boxing day sale compared to the prices of said magazines.