here are some sites you could add
- booru.allthefallen.moe
- derpibooru.org
- e926.net
- lolibooru.moe
- ponybooru.org
- realbooru.com
- sakugabooru.com
- beta.sankakucomplex.com
- twibooru.org
- xbooru.com
btw, i copied them from here https://github.com/Xwilarg/BooruSharp