Kiss PNG clear PNG
https://www.cleanpng.com/
I love IMG
https://www.iloveimg.com/
transparent textures
https://www.transparenttextures.com/
kawaii tumblr
https://koduck.tumblr.com/post/46788794969/some-people-have-asked-for-the-backgrounds-i-use
snappy tumblr
https://snaappy.tumblr.com/post/48487367697/super-mega-huge-background-pattern-texture-post
subtle patterns
https://www.toptal.com/designers/subtlepatterns/thumbnail-view/page/10/