You can still download an Urchin installer, but there’s a larger issue: you need a valid Serial Code to unlock the installation.
Urchin was officially canceled in 2012. If you have an active Urchin installation, here are your options:
1) Do Nothing
Keep Urchin on the same server and don’t move the data directory or upgrade the OS.
2) Migrate to Angelfish
You can migrate your Urchin config settings and report data to Angelfish Software.
If you still have your log files, a better solution is to only migrate the config settings from Urchin. Then reprocess the logs in Angelfish.