get removed the whole assembly from car brake booster + master cylinder go to shoba bazar in your town and see what you can get. The problem of zero brake at pedal pressure then 2nd push bring some braking is sign of damaged / leaking brake booster. master cylinder leakage has different sign. When you remove the booster also check for the VCV (vacum check valve) on the pipe running between intake manifold & boaster. BUY That VALVE NEW when replacing booster.
In pictures below you can see a master cylinder (metal cylnder with reservoir) detached from the brake booster (black round drum attached to firewall) & a VCV. Pictures are for reference only items in your car are of different dimensions