I want to replace the handle of this outside faucet but there is no replacement found in local hardware stores. If I can get the name then I could try to find it online
It's a typical Exterior Faucet Handle like these. This one happens to be Cello brand, but there's nothing special about it. That might not even be the original handle ;-) They tend to be pretty consistently standardized, so you should be able to use just about any kind of exterior faucet handle you can find.
This is what it looks like when it's off:
As you can see, you really just need any kind of handle that will fit however that shaft is keyed, and a nut to hold it on.
The most common names are sillcock, spigot, and hose faucet.