The best current production M1A mags, by far, are the USGI contractor CMI (Checkmate) mags. And 44mag.com has the best prices on them. They also make a stainless steel mag now that seems even more precisely made than the standard parkerized mags.
As for CDNN, it's your guess where they came from, but my bet would be they are Chinese; other possibilities include Taiwan T57 mags, and cheap US mags like Promag or Triple K. Some Chinese mags work, others don't. T57 mags are decent but USGI mags are better. I wouldn't take a chance on the CDNN mags.
BTW, I order from CDNN a lot and like them, but just like Sportsman's Guide, you have to take their product descriptions with several grains of salt - lots of stuff they describe as "GI" or "Mil spec" is only those in basic concept.