Makes sense. I hope the mags aren't Bidened before they become available. Sigh...The Shield Plus just got released and it's a new variant. Most likely, as with all new platforms and variants, all mags are being used for the new pistols.
You may not see any mags for a couple Months. And when they do hit the stores, remember... You are NOT the only one that bought a new Shield Plus. Everyone is going to be stalking the LGS, right along with you.
This has always been a side-effect for being someone that buys a new model.