[Koha] z39.50 host in new zealand

Dear all I just installed koha for our school, everything seems ok. I am sure my z39.50 works properly. The problem is the Z39.50 host. Many books in my school are about business,cookery, hospitality and English language. When I try to do a z39.50 search, always get the message of "Nothing found". I can only find a few of books. I am in New Zealand. Can somebody tell me some z39.50 server? The server I added are: National library of New Zealand National library of Aus Australia national university library.bangor.ac.uk library.hull.ac.uk Thanks for any help. Jenny