If a National company is not having Supply Chain, What would they need to start with to implement it? as it's important now after growing larger.

the success of a company depends on the service/s it provides.
A company which has the goal of becoming a leader in providing such services in any respective field needs to realize that flawless supply chain strategies secures their "image" to be as one.
Basically, a company needs a very versatile leader to head the department.
Have relevant data or information from the company's previous operation.
Infrastructures to accommodate the company's desired volume or services.

The supply chain is three types (Normal, Green & Cold).
You need first to know what is your sector and what products do you work with in order to establish its cycle.
Most of all you will need to create departments (Planning, Procurement, Production, Inventory Control/Warehousing, Logistics, Recycling for green chain).
You will need to have SOP's for each department and to connect all with an ERP system if possible.
The head of the supply chain department will be responsible to manage all cycle processes and the connection between all.
Please note that you will also need to involve the Sales department to get the customer satisfaction approval too.