Greenbone feed not getting updated to current status

“greenbone-nvt-sync --feedversion” gives me 202009151007.

feed.openvas.org is not reachable, so is feed.community.greenbone.net (at least there´s no ping reply).

OpenVAS is v9.0.3, this is the latest stable release coming with the Rasperry Pi OS/Debian Stretch.

Is there
a) a manual way of editing the feed source URL?
b) a Raspberry Pi compatible repository I can add to update to a newer version than provided by the default apt repository for my OS?