KWIK-KEY builds up to 9 alternate indexes from an existing VSAM file, and does it fast! You can also reload a base cluster and create up to 9 alternate indexes with a single read of the backup file. Direct CI processing (when available) also increases the speed significantly.
Is your batch window shrinking? Is moving to VSAM/RLS for all your files impractical? Try speeding up your rebuilds with KWIK-KEY.