I don't think the data are accessible as a CSV file, but try FINRA's Advanced Screener. It allows you to search for government, corporate, or municipal bonds using a wide range of criteria. FINRA also publishes TRACE Market Aggregate Information, which lists the most active investment grade debt securities and information about them.
For general information on both domestic and international debt markets, the Bank for International Settlements is a good place to start. They offer data in CSV format, although it isn't as specific as the data from FINRA's screener. For information about the US corporate bond market as a whole, you can also use the Federal Reserve Economic Data series of corporate bond data. FRED lists over a hundred series of yields on various classes and ratings of debt securities, all of which are available in CSV format, as well in XML format through an API.
I found a site that lists 101 Free Resources for Bond Investors; one section is devoted solely to bond market data. They list data sources like the FINRA data I linked to before, as well as sources specific to certain types of bonds, e.g. municipal bonds, Treasuries, corporate bonds, etc.