I finally got my hands on some Glock-made .40 22-round magazines. CDNN recently listed them on their website again, so I assumed they must be in stock again. I ordered two of them on May 18, they shipped the next day and I received them via Fedex on May 21.
I had long wondered what springs they used since they were shorter than 9mm 31/33-round magazines and none of the parts vendors list a specific spring for the .40 version. I opened one of the magazines up and discovered that they use the same 17-coil springs that the 9mm 31/33-round magazines use.
It was pretty difficult to get all 22 rounds into one, the other I could only get 21 rounds into. I haven't tried them at the range yet but they both hand cycle smoothly just as factory magazines should.
I had previously ordered some aftermarket KCI 31-round .40 magazines because I thought I'd never get my hands on Glock ones. I ordered a couple of Glock-made 31/33-round magazine springs to put in them, as well as some #9 followers. The original springs in those magazines are the same 17-coil springs used in the 9mm version. The followers were copies of Glock #8 followers. I tried a #9 follower in one but it didn't work very well, it would hesitate to rise fully at the top of the empty magazine. One of these aftermarket magazines has a Glock spring, the other has the original spring. Both hand cycle well until about the 24th round left in the magazine, then both magazines raise the stack of rounds very slowly and even to the point of the stack of rounds locking up and not rising all the way. Now I understand a possible reason for this, Glock used the same spring in a much shorter .40 magazine tube so maybe these aftermarket magazines need like 20-coil springs, which I don't even think are manufactured.