.TLD minimum number of nameservers rule

[nudgemac at fastmail.fm]

Sorry if this is slightly off-topic

I've just discovered that the TLD where I've registered my domain requires a minimum of 2 nameservers 
for any subdomain, which is very sensible but I happen to have a special case on my hands.
So I'd like to register a new domain elsewhere where they will allow a single nameserver execpt...
I cant seem to find out what the rules are for other TLDs. *before* registering.
Some kindly advise would be most welcome.