'Sure can do, but if you're willing to shell out another $11, we'll sell you a pair of drivers, wrapped in a headphone-shaped box - it even comes with a cable, ready to plug in!'
So, I guess AKG are like any other brand - after market is considered 'free money' and an invitation to fleece the customer...
(Though in fairness, for such a cheap-ish pair of headphones as the K240, the logistics of even keeping a spare inventory probably makes AKG lose money on selling me a new driver, even at the $70-ish price point I was quoted for a driver which goes into an $80 pair of headphones.)
Most companies don't bother keeping spare parts these days and if you, for some unknown reason, want to maintain your cheapish vintage cans, you should be AMAZED they still keep them in stock. Because they are definitely not making any money on it.