There is an undetected virus database that is claimed to be for ClamWin. The information manager for the site has offered access to the database to the R&D department of ClamWin. I am not affiliated with this site or its owner. I just happened across it while googling the net. Being an avid ClamWin user, I wanted to make the best contribution that I possibly could.

Go to:
https://viruspool.vanderkooij.org/undetected.cms

Select:
Clam AntiVirus

Then click:
Select

Within the page: "R&D crew of Clam AntiVirus please contact me, hugo(at)vanderkooij.org, if you need access to the sample collection."

Long live ClamWin!