Debian (sid): http://repos.rcn-ee.net/debian-riscv64/

deb [arch=riscv64 signed-by=/usr/share/keyrings/rcn-ee-archive-keyring.gpg] http://repos.rcn-ee.net/debian-riscv64/ sid main
#deb-src [arch=riscv64 signed-by=/usr/share/keyrings/rcn-ee-archive-keyring.gpg] http://repos.rcn-ee.net/debian-riscv64/ sid main

keyring:

apt-key adv --keyserver keyserver.ubuntu.com --recv-key D284E608A4C46402

Ubuntu (lunar): http://repos.rcn-ee.net/debian-riscv64/

deb [arch=riscv64 signed-by=/usr/share/keyrings/rcn-ee-archive-keyring.gpg] http://repos.rcn-ee.com/debian-riscv64/ lunar main
deb-src [arch=riscv64 signed-by=/usr/share/keyrings/rcn-ee-archive-keyring.gpg] http://repos.rcn-ee.com/debian-riscv64/ lunar main