It used to be https://www.twitch.tv/babymetalband, but now it’s https://www.twitch.tv/bifuteki3.
They only used it once in early April 2016 for this Q&A stream:
The ad also features an edited instrumental version of PA PA YA!!.
BABYMETAL is on the cover, and a condensed version of the main article in Issue 349, from July of this year.