What? Yes, Pak Suzuki doesn't have jack in stock, but the claim and price are both BS.
A thermostat is essential to maintaining the correct engine operating temperature, and using coolant is just as critical. Each component of your cooling system is there for a reason. This includes the humble radiator cap.
We Pakistanis are a scientific lot, with carefully thought-out explanations for why we use jugs of water from the Arabian ocean in our radiators, run our engines on packaged sludge (20W-50), remove our thermostats, and have the cooling fan running at all times, but we don't engineer a single motor vehicle suitable for export. I wonder why that is.
A brand new thermostat for your vehicle costs <Rs. 2500 and you can definitely find it. Just have to do some hunting. TAMA is one manufacturer for some quality aftermarket thermostats.
If you have the G10B 1000cc engine in your Cultus, the TAMA part number is W44DX-82 or W44DX-88. The last two digits indicate the thermostat's "beginning to open" temperature in degrees Celsius. You will need the right paper gasket to seal the thermostat housing once you put it back together.
If you don't already have a thermostat, use the opportunity to flush your cooling system and pour in the right amount and concentration of coolant when you install it.