How can I restore /system/bin/toolbox?

I accidentally removed /system/bin/toolbox on my Android 5.1.1 tablet. Right now I have temporarily replaced it by a busybox binary I had at hand, so the system is somewhat usable but not completely functional (e.g. no network connection). I have tried to pull the toolbox binary from other devices I have, but those are either Android 4 or Android 6, so it didn't work due to unresolved linker symbols. Is there a place where I can get a binary for a specific Android version? Or is there a place on my device where a backup is kept?