This is really for the moderator to respond, but as far as I know of there really aren't any sponsorship content your best bet is to try doing that type of thing through patreon access and linking itchio account with it.
As far as bundles go such as co-op bundles your best course of action is to join the itchio discord channel and look for " Join a bundle " and ask there for people to add you to the bundle, or you can always take a look at " games jams " https://itch.io/jams where occasionally a few users host a game jam where you submit your game or assets and they will make that into a bundle format.