That same thing is true of the Wright Brothers.
I’ve read that one unintended consequence of the AKs legendary toughness is that it’s hurting its current sales. Not many people need new AKs since the ones they have still work great. And in the case of the 7.62 MM AKMs, they don’t want to have to switch to the newer 5.45 round when they still have tons of the old ammo sitting around. Also, there’s no communist govt subsidy for AK production anymore. So they have to sell at a reasonable market price, which is much higher than in the past.
He reminded me of Mr. undershaft (“Major Barbara”): “This be the faith of an armorer, to make good arms, and sell to all who wish to buy them”.
His weapon was a big success-I wonder how many people were killed by it?
Very few. Its the bullet that gets em! 
What type of guns will they use?
The AK-47 and its derivatives are literally (as in actually, truly) the most common firearms on the planet. It’s impossible to get an accurate figure because the design has been so widely replicated but about 100 million is thought to be about right.
Just to put that in context, the next most produced longarm is the Mosin-Nagant M91/30 and its carbine variants, with a production figure of somewhere around 35-38 million. There were more than 17 million of the various Lee-Enfield rifles produced, about 15 million SKS rifles, and while a quick search didn’t turn up many reliable figures, about 8 million M-16 rifles have been made and it’d be a safe bet there’s easily as many AR-15s made as well. And, as a bonus piece of trivia, the civilian hunting/sporting rifle manufactured in the greatest quantities is the Winchester Model 94, with about 7.5 million rifles.
AK-47s might be tough but they’re not everything-proof. They will eventually break, rust, and wear out, especially if they’re not maintained at all. I do believe you’re right about the ammo issue, though - changing cartridges has historically been quite a difficult thing to do (it took the British about 40-odd years to get a replacement for the .303 round) and then you’ve got the problem of what to do with all the old ammo. Large countries can simply issue the old-calibre weapons (and ammo) to their reserve/second-line/cadet units, but the Republic of Sandistan probably doesn’t have that luxury and likely cannot afford to tip tens or even hundreds of millions of rounds of perfectly functional (albeit Cold War era) 7.62x39mm rounds into the harbour just so they can have a slightly newer version of the the same (again, perfectly functional Cold War era) rifles they’ve already got.
The international arms trade is a lot more regulated nowadays than it was back then, too - it’s quite hard for developing countries to offload surplus military longarms since most civilians aren’t allowed to own them anywhere and the militaries of most developed nations don’t need container-loads of Cold War vintage AK-47s from Sandistan, even for training purposes.
Also, back in the day, the “Government Subsidity” for AK-47 production was 100%. The rifles were literally given by the Soviets to any ideologically acceptable group who wanted them. I doubt there’d be so many AK-47s produced if they all had to be purchased commercially by the various entities which wanted them.
And to deal with that the company has come up with the AK-103, a current-standards version chambered for 7.62x39mm. Venezuela even bought a whole assembly line so they can continue to put together brand new ones locally (replacing locally-assembled FALs) but that seems to have been the one single big sale of the model. There are just too dagblastedly many AKMs out there. Heck, when Central/Eastern European countries moved to NATO and adopted NATO standards that in turn put another whole bunch of very well maintained high-quality AKMs into the market.