New replacement part may not be available locally, visit shershah (karachi's junk market) and buy a complete part i.e., solenoid + gasket as the shopkeeper may not sell the gasket alone. Whole assembly shall cost around 2500.
Better to take off the vtec solenoid from your car and keep it with you when searching for the gasket and/or solenoid, this will save your time in finding the right item.