VOLK is part of the GNU Radio ecosystem. Therefore, we use Matrix as our primary chat system nowadays. Find us on chat.gnuradio.org. Of course, most discussions will be on #gnuradio:gnuradio.org. Though, we have our own room #volk:gnuradio.org as well.
There is currently no mailing list dedicated to VOLK. For now either use IRC or the GNU Radio mailing list and use the predicate [VOLK] in your subject line.