"Shipping agent" means freight forwarder or ship agent. If you want to find a freight forwarder from New Zealand to Tonga, there are several ways you can:

　　International Freight forwarders  : There are many large international freight forwarders providing freight services from New Zealand to Tonga and all over the world. For example, DHL, UPS, FedEx and other internationally renowned logistics companies, they may have branches or agent networks in New Zealand and Tonga, can undertake sea freight transport, you can consult their official websites or customer service related business.

　　Online Logistics Platforms  : There are now a number of dedicated online logistics platforms that connect shippers with freight forwarders. You can post your shipping needs from New Zealand to Tonga on these platforms, and then the relevant freight forwarder will contact you with a quote and service plan.

　　Industry referrals and word of mouth  : Consult people in the trade and logistics industry in New Zealand or Tonga to find out which reliable forwarders they recommend. Or ask other experienced people in relevant industry forums and communities to obtain information and evaluation of freight forwarders.

　　Local New Zealand Business associations and Chambers of Commerce  : Contact your local New Zealand business associations, chambers of commerce or trade promotion agencies who may be able to refer you to experienced and reputable freight forwarders specialising in New Zealand to Tonga.