There's definitely some left, are you using the Itch.io client? It looks like the keys are only available if you sign in for the browser version of itch and then look at your library there
That's odd, I've tried it now and it shows up but only on the test copy I purchased myself - it doesn't seem to work for copies granted as a key, in case that's how you got it. If you mail me at stephengillmurphyty at hotmail dot com I'll manually send you on a code either way.
