I've made a repository for decals, most of them cleaned or recreated by hand by myself to make sure they look historically accurate.
It covers decals, from the usual NASA insignia variants to Chinese private startups like i-Space, and from Soviet spacecrafts to recent rockets like the recently launched Japanese IST MOMO5.
One thing this pack doesn't cover is the individual mission insignia, ship/mission names or engine markings - they are simply too numerous to compile - imagine individual Delta decals! What you will find is a lot of space agency insignia and corporation logos (aerospace-related or simply advertisements) in this pack.
You can download a zip or get individual images from here:
https://mega.nz/folder/XWRwAa5C#dlEnFoIJPXbsbQOeVjiiHA
