It depends on the country or region but popular way is to hit on the local chamber of commerce or department of commerce.
However, the most potential way is the traditional one, "Friends introduction".
In fact, ocean forwarding is the difficult field to make differences to others. If you have a strong advantage such as logistics, warehouse or good rate for such "After clearance service", it is easier. But friends introduction is the shortcut to gain trust and make difference to others.
I hope this hint supports you.
You have not enough information, but I can give some general suggestions.
1. I suggest you make to yourself a friends in that country, in where you looking customers, make many friends and they will help you in the future.
2. You can visit trade shows, exhibitions, fares.
3. You can connect with your country to ask help- Every country have ministry or trade departement, what focuses on expanding and increasing the export. They can help you and connect you with right people in your export destination country.
4. I have good experiences with ICC ( International trading organization), they can also help you