There are many other source definitions in McStas.
Detailed pulsed source components are available for new facilities in a number of contributed components:
SNS (contrib/SNS_source),
ISIS (contrib/ISIS_moderator),
ESS-project (sources/ESS_butterfly), the current, detailed time-of-flight moderator/target-station model for the European Spallation Source, superseding the earlier ESS_moderator_short (now in obsolete).
When no analytical model (e.g. a Maxwellian distribution) exists, one may have access to measurements, estimated flux distributions, or neutron event files. As of McStas 3.x, the recommended, portable way to read and write such neutron event lists is the MCPL format (see the misc/MCPL_input and misc/MCPL_output components, section 11.1), which has backends for McStas/McXtrace as well as several other Monte Carlo transport codes (MCNP, PHITS, Geant4, Vitess, SIMRES). The older, code-specific event-file components (Virtual_input/Virtual_output, Virtual_mcnp_input/Virtual_mcnp_output, Virtual_tripoli4_input/Virtual_tripoli4_output, Vitess_input/Vitess_output) still exist for backward compatibility but have moved to the obsolete component category (see the Component Manual’s Obsolete chapter); new instrument work should prefer MCPL.
Finally, optics/Filter_gen reads a 1D distribution from a file, and may either modify or set the flux according to it. See section ??.