Networking subreddits (r/ccna, r/networkingsimulators) or Cisco Learning Network forums sometimes have pinned posts with clean copies. You may also ask former instructors who kept the installer.
Want a small, easy-to-use simulator to practice routing, switching, and basic network services? Cisco Packet Tracer 5.3.3 is a great choice for beginners. It supports common devices (routers, switches, PCs), basic IOS-like CLI commands, VLANs, static and dynamic routing (RIP, OSPF), simple server/client services, and packet inspection for troubleshooting. The interface is intuitive and runs well on older hardware. Cisco Packet Tracer 5.3 3 Download
This version supports peer-to-peer networking, allowing multiple students to connect their virtual labs over a real network. How to Get Cisco Packet Tracer 5.3.3 Download Cisco Packet Tracer 5
While not available for public download on Cisco's modern site, version 5.3.3 can still be found on archival sites like the Internet Archive for historical or compatibility purposes. This version supports peer-to-peer networking