Car won't go out of park?

Car won't go out of park and even the mechanic can't fix it. The car is a 98 grand am. First the mechanic said the car needed a new shifter. The mechanic could not find a shifter for the car so he unlocked the shifter. The car was able to shift fine for a few days then it got stuck in park and when we banged on the shifter it came out of park. Took it back to the mechanic and he took the shifter out stuck his hand in it and jiggled the shifter and put it back in and said that should fix the problem. 5 days later and the car is stuck in park and banging on the shifter doesn't help. The brake lights come on and the brakes click but they wont go down. The car was hooked up to a diagnostic machine and the throttle position sensor was bad but the machine did not pick up anything else. The throttle position sensor was replaced. The car was slipping gears bad before the throttle position sensor was replaced. It seems the mechanic cannot pinpoint the problem with the shifter. The car will probably be stuck in park forever. Because a replacement shifter cannot be found can the old shifter be rebuilt? Is there anywhere on the internet besides ebay where a shifter for a 98 grand am can be bought? It is not the cable because the mechanic said that was fine. I do not know if he checked the fuses, brake switch or solenoids because he never said what he exactly did to the shifter the second time. It seems like I am being given the run around.