Depends how do you want to save and load them? Are you making RPG and want to save stats on Join / Quit?
There are few open source RPG projects that should have basic saving functions. This for example:
https://github.com/nokizorque/ucd/blob/master/UCDaccounts/accountHandling.lua
This resource has Kills & Deaths (adds them on scoreboard as well):
https://community.multitheftauto.com/index.php?p=resources&s=details&id=3472
Haven't tested it though, so not sure how it works.