Is there a list of wiki servers somewhere?
I once had a list and scanned it several times a day only to discover that the number of sites responding was highly variable. Around 1500 when I last looked. I also had a similarly sized list of sites that once responded but no more.
I kept similar counts for unique slugs and item ids which offers a more accurate measure of "size". When scanning content I would notice new sites mentioned on pages and add them to my list. Removing missing sites was more a matter of judgement for which I had no simple solution.
Here is a list of sites known to publish a recently vetted list of site on a page titled "Most Visible Federation".
paul.dojo.fed.wiki alanz.fed.wiki wiki.ralfbarkow.ch marc.relocalizecreativity.net found.ward.fed.wiki ward.dojo.fed.wiki wellspring.fed.wiki
A recent update of the vetting script will quietly share a list of sites that were once known but now have disappeared at the time each site chose to update their lists.