There have been at least 2250 known altcoins (a handful unlaunched). There's an overdue update of details of ~100 recently-launched alts but you can get an idea of the range from a text-only list of names/symbols: https://minkiz.co/coin/name/ or you can thrash your browser with the full display which includes a best guess at status of listed, defunct or extant (neither of the foregoing). Some of the listed coins have been subsequently delisted: https://minkiz.co/coin/
The raw data (in the form of an RDF graph) is available on https://github.com/DOACC/individuals, apologies in advance for the lack of documentation which is complete but needs updating with the latest data.
As an idle experiment, I'm keeping a few (those with <5 nodes) blockchains on life support: https://minkiz.co/acme, exactly as you describe.
Cheers
Graham