I know 3D artists have usually a kitbashing library made from 3D files they buy from asset packs.

But do 2D artists have something similar like a 2D library of drawings they can later photobash to save time?

>>7625914 (OP)
2d artists just save and use anything. 2d collage is has a longstanding history.
Most 2d asset packs are for use as-is or with minor modification. If you're melting images together to where they're not really recognizable then you don't need to pay anyone. 3 images overlaid into a mess with filters and shit, or 20+ images cut up and photobashed into a traditional-style "collage", doesn't matter. Just do what you want. The only thing you can really be dinged for is if you use a significant chunk of anything, or maybe if a trademark is clear and visible in a way that could confusingly imply the trademark holder endorses the image.

>>7625914 (OP)
there are brushes and shapes you can use
https://www.artstation.com/marketplace/p/8vqd/concept-generator-tool-custom-shape-mega-bundle-5200-pieces-photoshop
plus photos designed for photobashing, for textures, lights, masked photos for wires or fences etc.
pretty easy to make your own
you could use some 3d assets to make a 2d kitbashing kit too.