Many libraries have Moody's Municipal and Government Manual and Standard and Poor's Bond Guide, both of which provide information about individual issues of municipal bonds. Before you contact any broker about buying a bond, you should have a general idea of what kinds of bonds will meet your needs. If your broker offers bonds that don't fit your guidelines, be wary. It means that those are the bonds the firm has to sell, whether they're appropriate for you or not. Keep in mind, though, that you can't always get what you want.
Some traders have some of the bonds sometimes.
If there's a specific bond you want, you may be out of luck. Be flexible within the parameters you've set for yourself. Review what your broker has to offer. You can buy what's available, wait for new inventory, or try a different broker. If it's a buyer's market, you may be able to negotiate the price somewhat.