Yeah, writing those 25 bucks off is a good idea. I know it sucks to buy something with no apparent use completely by accident, and it would be nice if itch.io had a refund policy for cases like that, but so far, itch.io will only refund you in very specific cases.
Some pixel artists whose stuff I have lying around on my NAS are limezu, v3x3d and GuttyKreum. To my knowledge, none of them use generative AI. I've also made a game using this tileset: https://vurmux.itch.io/urizen-onebit-tileset.
Urizen is free and limezu's graphics are very affordable. The other two are a bit more expensive but still well worth the investment if you have an idea of what to do with them.
Aside from that, you can search itch.io with the "No AI" tag, e. g. https://itch.io/game-assets/tag-no-ai/tag-pixel-art