finding og assets seems to much tougher save for maybe googling tapastic mascot, tapas mascot or tapas mascot tapamon but finding hard ref sheets and like you mentioned the old media kit for tapastic is a bit tougher.
There may be a way to find it using internet archive but that depends on if the page itself was archived or if someone managed to find/create a snapshop (it'll also likely require backtracking to when the rebrand happened coz even i've kind of forgotten)
i will say i did find these two threads; one about the tapadog that contains the main tapamon's ref sheet and another about "tapamon lore" which contains some artworks of the other fellas
https://forums.tapas.io/t/tapamon-is-dead-long-live-tapadog/66325
https://forums.tapas.io/t/uncovering-tapas-lore/28805
there's also this page from koolaidqueen, tapas current/former graphic designer, that has some design notes and assets for branding they did for the site and social media
https://www.artstation.com/artwork/Pe1A34
not sure how much it helps but hopefully a good start