Some businessmen like to approach companies 'on spec' by letter or even in person, but this isn't usually necessary. Firms regularly advertise in trade journals such as World Trade Digest and Trade Winds Monthly, and of course on the Internet too.
Here are two examples, but there are many more.
Alibaba.com - The world's largest online B2B marketplace.
Import and Export on our award-winning International Trade Site. Find quality Products, Trade Leads, Manufacturers, Suppliers, Buyers and Wholesalers.
Asian Products--Import Export Directory for Importers, manufacturers, exporters,suppliers
Asian Products is a database and trade sources presenting products, manufacturers and suppliers to international buyers sourcing products in China, Taiwan, Hong Kong, Thailand...etc.
Many independent publications feature similar information (for example, in Talking Cents there is regularly listed US firms looking for overseas agents and distributors). Trade magazines can be found in business libraries, or direct from the publishers.
You can also make contact with manufacturers through trade fairs and delegations. Trade fairs are events where many firms will advertise products for export and advertise for agents, distributors and buyers.
Trade delegations are trips to countries organised for the specific purpose of developing trade contacts. These events are often promoted through Chambers of Commerce and via ads in trade journals.
Once you find a suitable manufacturer, contact them by fax, phone, e-mail or letter to express your interest in selling their goods. Ask for further details, including any available literature and samples, information on any other products available, and suggested markets.
If you're after an agency deal, ask about their commission rates and the price of the items. If you intend to buy and sell the goods, find out the wholesale prices and suggested retail price.