As for the tranny, Id say just go with a new one (from a parted car) all togther...you can come across them all the time here on max - if you need someone to install it, Im sure youve seen numerous posts about Charlie @ Bimmersport Automotive, hes the best when it comes to BMW's so Id recommend him as would 90% of this site im sure...
The bumper part...is it aftermarket or stock? maybe self tapping screws in the inside ... i really cant picture the porblem
For other parts (interior, dash, etc) send a PM to Temp - he has plenty of parts
Hope this helps
96' 328i M Tech | 15' 328i M Sport