Generally speaking, the typical consumer channels are great for obtaining radios, access points, and routers. But external antennas, adapters, pigtails, and cable can be harder to come by. On their quest for long-distance networking, many people find themselves dealing with general-purpose radio suppliers who have a great deal of knowledge about microwave gear, but very little experience with 802.11 devices.
Here is a list of popular suppliers for 802.11-related equipment. Among these vendors, you will find virtually everything you need for long-distance networking, from antennas and feed line to outdoor enclosures and weather proofing supplies. Many of them will build cables to custom lengths with whatever connectors you require, for a reasonable fee. They offer a nice selection of various 802.11-specific equipment, as well as general-purpose radio gear. These vendors are listed for reference only, and shouldn't be interpreted as an endorsement by either myself or O'Reilly.
With competition in the 802.11 market heating up, combined with the often confusing intricacies of wireless networking specifications, many vendors are realizing the importance of customer service. A good vendor should provide a great deal of information about their products online, and be willing to answer questions about your particular application.
Bluetooth, Mobile Phones, and GPS
Network Discovery and Monitoring
Wireless Network Design
Appendix A. Wireless Standards
Appendix B. Wireless Hardware Guide