WHOIS is not intended to be used to determine availability of domain names,
please use DAS for that purpose (or if you are offering registration via 1API
please use EPP check command via their interface).
DAS is available on the same server than WHOIS but on port 4343 and is not
rate-limited.
Please see http://www.dns.be/en/home.php?n=317 for description of DAS
protocol.
Basically:
echo "GET 1.0 ${DOMAIN}" | netcat whois.dns.lu 4343
