genuine thermostat valves are easily available at any dealership/showroom.
The parts seller shops treat spare parts like groceries, they only stock "running items like tune up and general small time repair items. Ask for a simple plastic clip worth Rs 0.50/- and they wont have it. Similarly because mechanic bhai doesnt want to buy Tstat valve they dont stock it.
In Pakistan - car spare parts only means filter, pilug, paaint, clutch, taming belt, faen belt, nothing more - ask for a genuine door card clip and they lose their minds, ask for an A/T clutch disc set or seal set and you get stares back like you have horns