How to add reload script into Roblox gears that don't have a reload?

You are gonna have to do it yourself, or you can commission someone

Inside the tool there will be a script/local script, find the script/local script which makes the gun shoot the bullets. After that insert a local script inside you're tool and paste this in:

local tool = script.Parent
local plr = game:GetService('Players').LocalPlayer
local mouse = plr:GetMouse()
local deb = false

local function reloading()
    if deb then return end -- tool wont work until it is done reloading
    deb = true

    script.Parent.Change_this.Disabled = true --reloading
    wait(1) -- change the number on how much seconds you want it to reload
    script.Parent.Change_this.Disabled = false --reloaded


    deb = false
end

tool.Activated:Connect(reloading)

After you pasted the script replace "Change_this" to the name of the script/local script that makes the tool shoot