We are working at making earlier versions of the Reactome database publicly available. In the meantime, MySQL copies of earlier database releases are available through the general URL structure:
https://download.reactome.org/XX/databases/gk_central.sql.gz
where XX is the version code for the release (ie 80 for Version 80, released 3/2022). See here for a list of Reactome version release dates.
Note that we are currently transitioning from a MySQL to Neo4J database. The current release of the database is available in both formats here.