These entries are queried from radb.net using whois, you can try my project getting these.
:AS-STEFAN6 as-set: AS-STEFAN6 descr: STEFAN6 NETWORK remarks: STEFAN6 NETWORK IPv6/IPv4 AS-SET members: AS206499 members: AS205591 members: AS-1STBB tech-c: MZ7290-RIPE admin-c: MZ7290-RIPE mnt-by: MAINT-AS206499 changed: noc [at] m-m-networks.net 20200620 source: ALTDB