Find exotic seed brokers online. There are a number of international suppliers that sell teak tree seeds, which are found in the Solomon Islands, Papua New Guinea, and other places off the coasts of Australia and Southeast Asia.
Contact a local certified arborist or arboriculturalist. Your local agricultural extension agent or a university agricultural extension office may be able to assist you.
Visit a nursery. Go to a local independent nursery and inquire about where to purchase teak tree seeds. Nursery operators deal with a wide variety of plants and trees and may give you contact information for a supplier. They may even be able to order teak seeds for you.