I have 2 questions,
1. Does anyone know where to get replacement parts for a 1998 Millenia? I am looking for a side mirror the whole peice.
2. I have a passenger side tail light that goes out only when you hit the brakes

 

Well, I can't help you with the parts you're after, but from your description it sounds like the brake light bulb (or portion of the bulb if a dual filament, like an 1157) is finding it's ground from the tail/running light and drawing away all the available current to it. It's creating a floating ground where there shouldn't be one.
To test, you could run a temporary wire from a body ground to the ground side of the brake light bulb and see if the other goes out when the brakes are applied then.