The IEM attempts a high fidelity processing and archival of Terminal Aerodome Forecasts (TAF)s. This page allows an atomic data download of the processed data. If you are wishing to download the raw NWS text TAF data, try looking here as a starting point.
Backend documentation exists for those wishing to script against this service. The TAF archive dates back to 1 January 1996.
Related: CWSU Center Weather Advisories Graphical AIRMETs PIREPs SIGMETs Temp/Winds Aloft