The only way to get a full listing of a DNS zone is to use AXFR to request a zone transfer. But that’s usually locked and not available. So building the zone file for a domain is basically guesswork or manual labour at best.
For some background information check out these questions on SO
Here’s a script I wrote to try and automate that as much as possible. Still in beta. Suggestions welcome.
Note: I use DNSPython
Next on my list is using the RimuHosting/Zonomi API to create/import the DNS zone.