In the secondary market, bonds are traded over-the-counter and in the bond trading rooms of stock exchanges and brokerage firms. Most are traded over-the-counter (OTC), meaning over the phone or on a computer. To make an OTC trade, a broker seeks a dealer who is currently offering the best price for a particular bond and negotiates a trade.
If you're looking for a specific maturity or yield, you may be able to buy directly from your brokerage firm, if the firm makes a market in that bond. If the firm doesn't hold an inventory in the bond, they'll make the trade through another dealer.
Because most bonds are traded OTC, where trades are made between individual buyers and sellers, it has historically been relatively difficult to find up-to-the-minute information about them. However, the bond market is becoming increasingly transparent. In 2002, FINRA launched the Trade Reporting and Compliance Engine (TRACE), which reports approximately 90% of all OTC bond trades within five minutes. The municipal bond market became easier to track in 2005 when the Municipal Securities Rulemaking Board began offering real-time information on their Investing in Bonds Web site. Though these two systems are making bond trading much more transparent than in the past, bonds that are infrequently traded can still be hard to follow.