_pgpkey-http._tcp.au.gnupg.net. SRV 0 0 11371 keyserver.zap.org.au.
_pgpkey-http._tcp.au.gnupg.net. SRV 0 0 11371 svcs4.riverwillow.net.au.
_pgpkey-http._tcp.au.gnupg.net. SRV 1 0 11371 keys.keysigning.org.
_pgpkey-http._tcp.au.gnupg.net. SRV 0 0 11371 keyserver.oeg.com.au.

$ gpg --no-options --keyserver hkp://au.gnupg.net --search-keys 0xA29A84A2
gpg: error searching keyserver: Unknown host
gpg: keyserver search failed: Unknown host

Note that using a DNS label which has A and/or AAAA records in addition to SRV
records (e.g. keys.au.gnupg.net) works because although dirmngr ignores the SRV
records, it finds the address records.

This SRV support was present in the old libcurl implementations and still works
in 2.0.26 and 1.4.18.

Also note that I found the following in dirmngr/ks-engine-hkp.c:

  813:  else
  814:    {
  815:      /*fixme_do_srv_lookup ()*/
  816:    }

See also this thread in the gnupg-devel mailing list:

http://lists.gnupg.org/pipermail/gnupg-devel/2014-December/029185.html