Somebody help

Hello, all my Mustang people. Im curently have a problem, my car is being a trick. The tranny tends to slip outta gear & when i hit the gas its like im in neatrul. I know its the MLP sensor, but my problem is. I dont know where to get one. Ford said they would do it for me for like close to $300(part & installation). I know there has to a company out there that makes these things.

Cant you just go to the parts department at the local ford dealer and buy the part?