mostly, i just search for the things i like such as sanrio, splatoon, my little pony, lps, madoka, cookie run, etc. etc. and add "gif" and/or "transparent" or for more general things: "tropical" "aesthetic" "kawaii" + "pixel" or "gif" . i try to find the sources and see if the people who posted them have more that i can find :>

as for my stamps, i get all of them on deviantart just by typing a thing i like + "stamp", or i look through people's favorited collections of gifs