Vauxhall corsa gearbox?

Hi there my vauxhall corsa needs a new gearbox do you know anywhere where i can get a used gearbox which is in good condition to fix into my car and roughly how much do you think this job will cost. It is an automatic car made in 1998 1.4l the car can still drive manually as there is a sports light flashing while im driving how long do you think the car will be able to drive as it needs a new auto gearbox