Lainchan site suggestions

https://society6.com/ -For stickers not sure about shirt quality
https://www.redbubble.com/ -Good for stickers, shit shirts though
https://www.teepublic.com/join/mannypdesign -Good for stickers, and shirts
https://merch.amazon.com/landing -Honestly don't know if they do stickers but they do shirts BUT you need to be approved.
https://www.threadless.com/ - A Lainon actually posted from this site in a merch thread, seems like good shirts.